OṄKĀR, generally written down as Oaṅkār in Sikh Scriptural writings, is derived from the Upaniṣadic word Oaṅkāra (om+kāra) originally signifying pronouncing or rendering into writing the syllable Om. Known as synonym of Om it has been used in the Vedic literature and, in particular in its religio-philosophical texts known as the Upaniṣads, as a holy vocable of mystical signification and as the most sacred of the names of Brahman, the Supreme Self or the one entity which fills all space and time and which is the source of the whole universe including the gods themselves.

         The word om, the most hallowed name of Brahman, is derived, according to the Gopatha-brāhmāna (I. 24), from āp ‘to pervade' or from av 'to protect'. This monosyllable is said to command the highest Spiritual efficacy for the realization of the Supreme spirit. Considering Brahmā (a) to be inhalation; Viṣṇu (u) to be suspension, Rudra (m) to be exhalation, the prāṇāyām is also indicated as obtainable by concentration on Om.

         The three sounds (AUM) have been described as symbolizing the material, the subtle and the causal world respectively (Mān. Up.., 8.11). This interpretation envisages the comprehension of the entities of matter (prakritī), spirit (jīva or ātman) and God (Brahma) within the concept of Om or Oaṅkāra. The three sounds have also been identified with three quarters of Brahman representing, in their respective order, His waking, dreaming and sleeping states, His fourth quarter, all pervading Oaṅkār, having been described as transcending all conventional dealings and the phenomenal world (Mān. Up. ., 9.12). Amidst the kṣara or perishable objects of the phenomenal world, He is ekākṣara, the Sole Imperishable One (Atharvaveda, V. 28. 8; BG VIII, 13).

         According to the Upaniṣadic seers, the word Om, known as Praṇava also, serves as an aid or a medium to the meditation on, and the realization of, the Supreme Spirit (P. Up. V. 5; Śv Up. I. 13-14; Kaṭhā Up. I. 2.17). The Muṇḍaka Upaniṣad (II. 2.3.4) metaphorically describes Praṇava or the Oaṅkāra as the great bow which helps the arrow in the form of soul, sharpened with meditation, reach the target, that is, the Imperishable Brahman. According to the Śvetaśvatara Upaniṣad (I.13), the Universal Spirit is realized through Oaṅkāra just as the form of fire is realized through the fuel. Identifying Oaṅkāra, the name or the signifier, with Brahman, the object signified, the seers imply that meditation on Oaṅkār means meditation on Brahman. The Māṇḍūkya Upaniṣad accepts syllable Om as "all that is past, present or future, and whatever is beyond the three periods of time is also verily Om."

         The pantheistic concept of Brahman as the Supreme Self, one and impersonal in character, and often identified with Om or Oaṅkāra, continued to hold good along with the growth of the polytheistic concept of the personal gods like Brahmā, Viṣṇu and Śiva, the two concepts acting and reacting and complementing each other in the long history of the religio-philosophical tradition of India.

         Gurū Nānak, in order to emphasize the strict monotheism of the creed he was preaching and to discountenance any possibility of the kind of polytheism prevalent in India reasserting itself, added the numeral 1 (one, pronounced as ek in most Indian languages), the Formula for the Supreme Being thus emerging from his revelation as Ek Oaṅkār. To this numeral one (ek or ik) a mystical significance attaches in the Sikh creed. Besides being the opening sentence-phrase of the Mūl Mantra, standing at the head of the Gurū Granth Sāhib, Ek Oaṅkār emphasizes the Nirguṇa (the unattributed) character of Brahman, the Supreme Being. Ek or Ik in this formula is called bīj-mantra or the seed formula, out of which has grown the entire fabric of Sikh creed, which totally discountenances any polytheistic or even what is known as the henotheistic concept. This Ek is the very image of the Supreme Being, the Divine Essence (śuddha svarūpa), accepted in Gurū Granth Sāhib. Bhāī Gurdās, the great savant and poet, thus expresses the relationship of Ek with Oaṅkār : "The creator first manifested the One; and after, set by its side the ’ūṛā' 'Oaṅkār' (Vārāṅ,III.15). For 'O' the original is ūṛā, the first neuter vowel-letter of the Gurmukhī alphabet, representing according to its diacritical mark 'O' or 'U'.

         From the above it will be indicated that the numeral Ek with Oaṅkār is all-important emphasizing the attributelessness, soleness and transcendence of Brāhmaṇ, also known in Sikh theology as Pārbrahma 'transcendent Brāhmaṇ'. Among the names of the Supreme Being primarily belongs Ek Oaṅkār, which is repeated in Mūl Mantra by the initiates to Sikhism, when taking amrit.

         A distinction exists philosophically between Ek Oaṅkār and Oaṅkār. Ek Oaṅkār being the unattributed, transcendent aspect of the Supreme Being, Oaṅkār is the attributed (saguṇ, sarguṇ) aspect, the Creator, to whom devotion and worship may be offered. In the Sikh creed the Supreme Being is both 'attributed' and 'unattributed', no distinction being made between His two aspects — attributed aspect not represented by any deities or such other beings. The combination in Him of both aspects is emphasized in Sukhmanī (GG, 287, 290). In numerous places in Gurbāṇī the combination in the Supreme Being of transcendence and immanence, the unattributed and the creative (attributed) aspect, is emphasized through various images and similies. Māhā Kavī Santokh Siṅgh, in his Ṭikā Garab Gañjanī affirms that Oaṅkār, the creative aspect of the Supreme Being is Brahmā associated with māyā. In the hymn Rāmkalī Dakhṇī Oaṅkār, at the very outset, the Creator is saluted as Oaṅkār. Gurū Āmar Dās in Mārū Solahe (18), affirms : "Oaṅkār sabh srisṭi upāī— Oaṅkār created the universe. Bhāī Gurdās (Vārāṅ, XXXVII. 1) represents Oaṅkār as the Creator. He further endorses that by becoming and uniting Śiva and Śakti, the creation is brought about by Oaṅkār. Ik Oaṅkār is likened to the sun which shines in sole splendour, while the manifest universe is likened to the numberless stars. In Vārāṅ, 26. 2, the melody of the word rising from Ek Oaṅkār is said to have created the Oaṅkār (with attributed form). In Vārāṅ, 29.19, Bhāī Gurdās recounts three stages of the Supreme Reality. They are : Niraṅkār, Ekaṅkār and Oaṅkār. Niraṅkār being the Suṅn Samādhī (seedless trance) stage, Ekaṅkār and Oaṅkār may be considered as grosser stages of the Niraṅkār Brāhman, in and through which He creates the cosmos. This elucidation by Bhāī Gurdās is consistent with Gurū Nānak's thought in Vār Asā where he expounds : "āpīnai (Niraṅkār) āpu sājiu (Ekaṅkār) āpīnai rachio nāu (Oaṅkār) dūī qudarati sājīai (creation from Oaṅkār) kāri āsaṇu ḍiṭho chāu (all pervading Niraṅkār creative as Oaṅkār)." It may be further noted that all the three aspects of Aphur Brahman, i.e. Nirankār, Ekaṅkār and Oaṅkār, have been delineated as creators by saying "Oaṅkār sabh srisṭi upāī" (GG, 1061), "Niraṅkār ākāru upāiā" (GG, 1065) and "Ekaṅkāru eku pāsārā ekai apār apārā" (GG, 821). In Vārāṅ, 18.12, also Oaṅkār is presented by Bhāī Gurdās as the Creator. To contrast with Oaṅkār, terms Niraṅkār (the formless) and Nirādhār (the absolute) are used. In Sukhmanī (GG, 276, 284), after creation is dissolved, the Supreme Being remains Sole Absolute (Ekaṅkār, Ik Oaṅkār). Gurū Gobind Siṅgh also, in Akāl Ustati, salutes the Absolute by saying : 'praṇvo ādi ekaṅkārā' (I bow to the Primal Absolute).

         The signification attaching to Ik Oaṅkār must have become clear, which while using the syllable Oaṅkār from Upaniṣadic literature has given to it a meaning and conceptual content different from what it bears in those texts.

         This concept of Ik Oaṅkār (the Sole Oaṅkār), also written down as Ekaṅkār (GG, pp.153, 276, 608, 736, 838 etc.) represented by the holy syllables (1) in the Granth Sāhib, is the basic tenet of the Sikh religion and its theology. This symbol precedes the Mūl Mantra or the basic formula of the Sikh theology, prefixed to the Japu and all the musical measures in the Gurū Granth Sāhib. The Mūl Mantra enunciates in succinct form, the concept of Ek Oaṅkār, who is the Sole Supreme Self, the Truth Eternal, the Creator of all and Self-existent. While defining Him, the Mūl Mantra, uses some negative terms also. Thus He is described as Nirbhau — without fear; Nirvair — without rancour; Akāl – Mūrati — form eternal; Ajūnī — not subject to the cycle of birth and death.

         This concept of Oaṅkār has been expounded in elaborate and inspiringly sublime form in the Gurū Granth Sāhib which time and again has put a special emphasis, in view of the socially as well as the spiritually disintegrating thought necessitated by the prevailing circumstances, on the oneness of the Supreme Being. It is only with reference to His infinite creation or the multiplicity of the beings, both animate and inanimate, created by Him that He has been described as anek (not one, i.e. many) and saguṇa in the Gurū Granth Sāhib; otherwise, primarily, He has been conceived and described as nirguṇa. Nirguṇa Aphur Brahman in Sikhism being Saphur, without changing His transcendent character and stimulating His creative divine power, Oaṅkār, which hitherto was latent and unmanifest, creates the cosmos by assuming the role of the Kartā-Purakh. He is not that Niraṅkāra becomes sākār in any gross sense; he rather, in the Gurū Granth Sāhib, is explained as a creative divine power. In Indian philosophical and theological thought where av is considered as the root of Om, the emphasis is laid upon its protective aspect, whereas in Sikh Scripture its creative divine power has been taken into account.

         Of the other terms considered equal to Oaṅkār or Brahman, the term sat and its cognates satya and sach being the basic need of a spiritually as well as socially well knit society, get a preferential treatment by the Gurūs in the Gurū Granth Sāhib.