The meaning of the Gayatri Mantra is more a prayer than revealing the essence of the Vedas. Gayatri mantra is said to be mother of Vedas meaning the mantra points to the full import of the Vedas. But the meaning does not suggest what the Vedas have to say except here and there to give the attributes of God and praying to that God to illumine us.

So let us meditate on Gayatri Mantra to find out the true Vedic meaning:
The accepted meaning of Gayatri Mantra is as follows:

OM :- Pranava - The word that is God
BHUH :- God who is eternal
BHUVAHA :- God who is the creator
SVAHA :- God who is Independent
OM TAT :- That eternal God
SAVITHUR :- That creative principle of light manifested through Sun
VARENYAM :- That Supreme God propiated by the highest Gods
BHARGO :- That light that bestows wisdom, bliss and everlasting life
DHEVASYA :- The light of that effulgent God
DHEEMAHI :- we mediate
DHIYO :- May our intellect
YO NAHA :- Be directed by that lord
PRACHODAYAT :- Towards Illumination

Freely rendered the meaning should suggest the following.:

OM, thou my supreme lord, my innermost SELF, mayest thou open my mind and make it receptive to comprehend the deep meaning of thy word OM and enable me to purify my mind so as to unlock the door to wisdom! May my consciousness be free to experience that pure and immaculate awareness, and be able to abide in that absolute SELF. May all my propensities be erased to make me ready for the holy immersion into the supreme taintless immutable SELF. OM

Gayatri Mantra indicates the knowledge of the essential Oneness of the self in each of us and self everywhere.

Yonaha --- Our
Dhiyo (Dhiyaha --- Intellects)
Prachodayat --- (prerayetu inspire)

The one who illumines all activities of the subtle body (mind, intellect ego etc) and remains itself as a mere uninterferring " witness" is the inner self. Thus the word sound Prachodayat indicates the Atman. Through the Tat Savitur sentence the real Brahmin is established. The supreme Brahman alone is the self, invoking whom the prayer "inspire us" (Prachodayat) was raised. The self is indicated in the Gayatri Mantra by the term Sun (savituhu the effulgent light). Here the word "THAT (TAT) " indicates the Self evident, Self within which is nothing but self in all, the supreme self. That thou art--- tat thvam asi

The term Savituhu (Sun) indicate the One Substratum for all the delusory experiences of plurality and their illusory play in the field of creation-sustenance-and - destruction). Worshipful, adorable, (varenyam) means, " That which is courted by all" as It is the nature of Infinite Bliss. Resplendent (bhargaha) here is indicative of the knowledge, which will destroy avidya and its associated rajas and tamas. The Light (devasya) here suggests the ever-present Pure Consciousness illuminating everything. The terms Sun (Savituhu) and light (Devasya) are used in constructive meaning " Sun's Light" the consciousness of the self. The term "Dheemahi" is the Vedic construction for "we meditate" (dhyayem). Now it is clear that the Gayatri-mantra indicates in its deeper meaning the invocation of the supreme self, which is the sum, and substance of Vedas and Upanishads. Therefore the name Veda Mata for Gayatri is justified.

Let us look into the meaning of the VYAHRUTIES.

Bhuh indicates the permanent. The all pervading One that exits at all period of time, the self is invoked by this term. The term Bhuwah suggests Pure Consciousness due to the etymology of the term: Bhuwah comes from "imagines" (bhavayati) suggesting the awareness that illumines our thoughts. Swah in its import suggests one own essential reality. The term Mahah directly suggests the "most glorious" or the "most wosshipful" which is the Supreme self. Jana derives from "creates" (janayati) suggests that which is the "One Cause" for all names and forms, within and without. The term Tapah means resplendent-splenderous full of brilliancy. The Self as Consciousness alone the source of all light in the Universe. Satyam is a state that is beyond the pale of sorrows and pain. Thus the seven Vyahruties are described as the seven "Worlds" meaning the field of experiencees

NOW: Therefore as we said earlier that Gayatri indicates the Infinite reality. The self which is the pure Existence, which is the meaning indicated by the Vedic mantra OM, signifying Brahman, Bhuh etc., all the seven worlds are also comprehended in OM- meaning and Brahman alone is meant here.

The above commentary about the Gayatri Mantra is by Adi Sankara and rediscovered by Swami Chinnmayananda during his travels in Himalayas in the hands of a Brahmin in Devaprayag.

The Sanskrit text of Adi Sankara's commentary follows.

Nah - asmakam Dheeyah - Buddhi Prachodayat- prerayet
Sarvabudhi samgnanthah karana prkashakah sarva sakshi prethyagathma iti uccyathe
Thusya prachodayatu sabdanistasya atmanah
Swarupabhutam param brahma tat savitur ityati padayh nirdisyateh
Atra tat subdena prthyagbhutam swatah siddham param bramhma uccayathe
"Savituriti" srustistitilayam lakshnasya sarvaprpanjasya dwaitabhavasya adistanam lakshyate
"varenyamiti" sarvaraneyam niradhshayaandarupam
"bharga iti" aviyatidosabharjanatmakam gyanaikavishayathwatu
"devasya iti" sarvathyadhothanathmakaakandachitekarasam
savitudevasya ityatra sastayarchi rahoha shirovatu oupacarikaha
bhdhyati sarva dhrisyasya sakshilakshanan
yanme swarupam thath sarvadhristanarupam paramanandam
nirastasamasthanardharupam swaprkashachitatmakam brahma ityevam
dhimahe - dhiyayeth
evam sathi praytyagatmanaha brahmana saha thatahtmarupamekatvam bhavathi
thayaa sarvathmakabrahmabhodakosyam gayatrimantraha sampatyate

atah saptavyahritinam ayamarthah

"Bhuriti" nityatvam uchyate - thatha hi sarvavyapi sarvakalikam
sarvorthkusta nityamuktam atmasvarupam anmatra uchyate
"bhuvha" iti sarva bhavayati prakshyati iti
vuthpatya chitrupatvam uchyate
"sawriti" srusti sarvaha veramansyarupam uchyate
"maha iti" mahiyathe pujyata iti vyuthpathya sarvatshyatvam uchyate
"jana iti" janyatheethe vyuthpatha sakalakaranatvam uchyate
"thapa iti" sarvatejorupam
"atyamiti" sarvabhatarahitam
yetadhktuktam bhavati
satrupam thadhu Omkaravachasya brhamayva bhurathayaha sarva lokaha
Omkaravachyabrahmatkaaha na thatrayatirikta kichidhasthi
Iti vyahruthayospi sarvathmabrahmabhodhikaha

Let us look at the mantra words from another Upanishad :

Tripura-Tapini-Upanishad

I praise that Supreme Truth which is Knowledge Absolute, which is to be known
through the Vidya of the Tripura-Tapini-Upanishad.
The Lord assumed the form of destructive ferociousness and then He covered
Himself all over the three worlds, Bhuh, Bhuvah and Svah. Then He had that
power of the Adi-Sakti, i.e., the Adi-Sakti burst out from His heart. This is
The Sakti called the Maya of Siva and She is understood by the fundamental
syllable 'Hrim'. This Sakti then covered the whole universe. Since She
Covered the three worlds or Tripuras, She has been styled as 'Tripura'.

This Tripura Sakti has the following Vidya called Sri Vidya, which can be
Derived from the following Vedic Mantras:

TATSAVITURVARENYAM BHARGO DEVASYA DHEEMAHI | DHIYO YO NAH
PRACODAYÀT | PARO RAJASE SÀVADOM |
JÀTAVEDASE SUNAVÀMA SOMAMARÀTÃYATO NIDAHÀTI VEDAÞ |
SANAÞ PARÙADATI DURGÀÕI VI÷VÀ NÀVEVA SINDHUÜ DURITÀTYAGNIÞ ||
TRYAÜBAKAM YAJÀMAHE SUGANDHIM PUSTIIVARDHANAM |
URVÀRUKAMIVA BANDHANÀTHMIRTYORMUKTIYA MÀMRITÀT ||

This Vidya consisting of one hundred letters is the Supreme Vidya in its entirety. This is Paramesvari, Tripura Herself. Out of the above Mantras, the first four stanzas deal with the exposition of the glory of the Para-Brahman. The second set of stanzas deals with the Mahima of Sakti. The third set deals with the glory of Siva Himself. In this Vidya, all the worlds, all the Vedas, all the Sastras, all the Puranas and all the Dharmas have been dealt with and this is the Effulgence that has come out of the combination of Siva and Sakti.

Now, we shall comment on the most important and the hidden meanings of these verses.

Here the great word 'Tat' means Para-Brahman Itself, the Eternity. This is the symbol used for that Lord who is beyond all definitions and arguments. This Lord is the embodiment of Supreme Knowledge itself. That is, He wishes to be in the form of Knowledge Absolute. He alone is the great Lord Siva who is always desired by sages, Yogins, etc., in Yajnas. Therefore there is the creation of desire. Thus, this Lord who is beyond the reach of all desires, still desires and is being desired. He creates the alphabetical list of language. Therefore, the Lord is called 'Kama' or desire. The letter representing Kama is called 'Ka'. Therefore the word 'Tat' represents the letter 'Ka'. This is the meaning of the word 'Tat'.

'Savituh' comes from the Sanskrit root-word 'Sunj Praniprasave', which means the Generator or producer of all beings. He is the great Power. Power means Sakti. This great Sakti or Devi called Tripura, is embodied in the Mahakundali (Yantra). Thus, the fire-globe (of the sun,Savituh) should be known by the intelligent. This Sakti or power of Trikona (triangular figure) bears out the letter called 'E'. Therefore we should learn the word 'E' from the word 'Savituh'.

'Varenyam' means that which is fit to be adored and worshipped, which is the imperishable and the praiseworthy. Therefore, it should be understood that the letter 'E' should be taken from the word 'Varenyam'. 'Bhargo' and 'Dhimahi' will be now commented upon. The letter 'Dha' means Dharana or concentration. The Lord is always concentrated upon by the 'Dhi' or the intellect or Buddhi. 'Bharga' is the Lord Himself who can be understood only by reaching the fourth stage or Avastha and this is the Being that pervades all and all. The letter representing this fourth stage is called 'I' and this is the real meaning of the above-mentioned words of the Mantra. We shall now talk of the word 'Mahi'. 'Mahi' means greatness, idleness, strength, stubbornness, and this applies to that element which possesses all these qualities. That is the earth which is represented by the letter 'La'. This is the Supreme state. Thus, this Lakara shows the quality of the earth in its being the embodiment of all oceans, forests, mountains and the seven islands. Therefore the form of Devi called the earth, is termed 'Mahi'.

Now about 'Dhiyo Yo Nah Prachodayat'. Para or the Supreme is the Imperishable Siva Himself, the Eternal Soul. The underlying meaning here is this: We should meditate on the immobile form of Lakara or Jyotirlinga or Lord Siva which is the most supreme thing that ever exists anywhere. Here, there is no desire for any Dhyana whatsoever. It is beyond all Dhyanas. Therefore, we are requesting the Lord to direct our minds to be established in that Nirvikalpa State where there is no thinking at all. This request should not be made through the mouth. It should be simply thought of in the mind. Then 'Paro Rajase Savadom'. After meditating on the form of the Supreme Truth, there will come out a big effulgence, pure and blissful, full of knowledge which is residing inside the heart. This is the essence of all speech and Knowledge. This is the true Sakti. And this is called the Panchakshara, since it is the creator of the Pancha Bhutas or the five elements. This should be understood correctly by the intelligent.

This is the Vidya giving all desires to the devotee. Thus, after understanding in its true aspect, this Vidya of thirtytwo letters, the devotee Should think of the letter called 'Ha' which is the form of Siva, who is the Imperishable, pure State. The letter derived out of the combination of the sun and the moon, that is, the combination of Siva and Sakti is 'Ha' and it is also named as 'Hamsa'. This is the seed of Kama. Through this Vidya, we can know the Supreme Lord Siva. This combination is also understood as being the merging of the Jivatma in the Supreme Paramatman. Thus 'Ha' means the Eternal Stage or the Final Emancipation. This is the derivation of the Sri Vidya. One who knows this, attains the form of Rudra. He bursts open the residence of Vishnu and reaches the Para-Brahman.

Thus we can understand that the Tripura Tapini Upanishad directly points to the Para Brahman, the Mantra words of the Gayatri.