संस्‍कृतशब्‍दकोशः

ओम्

पवित्र अक्षर‚ प्रणव‚ ब्रह्म‚ अनुमति‚ हाँ‚ अंगीकार और उपक्रम का द्योतक अव्यय

sacred syllable om, expresses : affirmation or assent, yes, so be it

Monier–Williams

ओम् — {óm} ind. (√{av} i, 141##originally {oṃ} = {āṃ}, which may be derived from {ā} ), a word of solemn affirmation and respectful assent, sometimes translated by 'yes, verily, so be it' (and in this sense compared with Amen##it is placed at the commencement of most Hindū works, and as a sacred exclamation may be uttered {but not so as to be heard by ears profane} at the beginning and end of a reading of the Vedas or previously to any prayer##it is also regarded as a particle of auspicious salutation [Hail!]##{om} appears first in the Upanishads as a mystic monosyllable, and is there set forth as the object of profound religious meditation, the highest spiritual efficacy being attributed not only to the whole word but also to the three sounds {a}, {u}, {m}, of which it consists##in later times {om} is the mystic name for the Hindū triad, and represents the union of the three gods, viz. a (Vishṇu), {u} (Śiva), {m} (Brahmā)##it may also be typical of the three Vedas##{om} is usually called {praṇava}, more rarely {akṣara}, or {ekākṣara}, and only in later times {oṃkāra}) &c##(Buddhists place {om} at the beginning of their {vidyā ṣaḍakṣarī} or mystical formulary in six syllables [viz. {om maṇi padme hūṃ}]##according to {om} may be used in the following senses: {praṇave}, {ārambhe}, {sviikāre}, {anumatau}, {apâkṛtau}, {asviikāre}, {maṅgale}, {śubhe}, {jñeye}, {brahmaṇi}##with preceding {a} or {ā}, the {o} of {om} does not form Vṛiddhi ({au}), but Guṇa ({o}) 6-1, 95.)