Om

Webster's Dictionary

(interj. & n.) A mystic syllable or ejaculation used by Hindus and Buddhists in religious rites, - orig. among the Hindus an exclamation of assent, like Amen, then an invocation, and later a symbol of the trinity formed by Vishnu, Siva, and Brahma.

The Nuttall Encyclopedia

A mystic word among the Hindus and Buddhists; presumed to be latent with some magic virtue, and used on solemn occasions as a sort of spiritual charm efficacious with the upper powers, and potent to draw down divine assistance in an hour of need.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature

a Sanscrit word of asseveration, much used in Buddhistic works as an introductory term. It is especially prominent in Lamaism (q.v.).