Om
Pronunciation

When occurring within spoken Classical Sanskrit, the syllable is subject to the normal rules of sandhi in Sanskrit grammar, with the additional peculiarity that the initial o of " Om " is the guṇa vowel grade of u, not the vṛddhi grade, and is therefore pronounced as a monophthong with a long vowel (), ie. ōm not aum. Furthermore, the final m is often assimilated into the preceding vowel as nasalisation (raṅga). As a result, Om is regularly pronounced in the context of Sanskrit.

However, this o reflects the older Vedic Sanskrit diphthong au, which at that stage in the language's history had not yet monophthongised to o. This being so, the syllable Om is often archaically considered as consisting of three phonemes: "a-u-m". Accordingly, some denominations maintain the archaic diphthong au viewing it to be more authentic and closer to the language of the Vedas.

In the context of the Vedas, particularly the Vedic Brahmanas, the vowel is often pluta ("three times as long"), indicating a length of three morae (trimātra), that is, the time it takes to say three light syllables. Additionally, a diphthong becomes pluta with the prolongation of its first vowel. When e and o undergo pluti they typically revert to the original diphthongs with the initial a prolonged, realised as an overlong open back unrounded vowel (ā̄um or a3um). This extended duration is emphasised by denominations who regard it as more authentically Vedic, such as Arya Samaj.

However, Om is also attested in the Upanishads without pluta, and many languages related to or influenced by Classical Sanskrit, such as Hindustani, share its pronunciation of Om (or).
combination:two_responses, detectable_format:number_highlighted_sections[2]