The Collaborative International Dictionary of English v.0.48:

Om \Om\, interj. & n. [Also Aum, Um.] [Skr. [=o]m.]
   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.

   Om mani padme hun, a sacred formula of buddhism (esp. of
      the Lamaists) translated "O, the Jewel in the Lotus,
      Amen," and referring to Amitabha, who is commonly
      represented as standing or sitting within a lotus.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Aam \Aam\ ([add]m or [aum]m), n. [D. aam, fr. LL. ama; cf. L.
   hama a water bucket, Gr. ?]
   A Dutch and German measure of liquids, varying in different
   cities, being at Amsterdam about 41 wine gallons, at Antwerp
   361/2, at Hamburg 381/4. [Written also Aum and Awm.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Aum \Aum\, n.
   Same as Aam.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Aum
    n 1: a terrorist organization whose goal is to take over Japan
         and then the world; based on a religion founded in 1987
         that combines elements of Buddhism with Christianity; "in
         1995 Aum members released deadly sarin gas on a Tokyo
         subway train" [syn: Aum Shinrikyo, Aum, Supreme
         Truth]