Source : Webster's Revised Unabridged Dictionary (1913)

Mantra \Man"tra\, n. [Skr.]
   A prayer; an invocation; a religious formula; a charm.
   [India]

   Note: Among the Hindoos each caste and tribe has a mantra
         peculiar to itself; as, the mantra of the Brahmans.
         --Balfour (Cyc. of India).

Source : WordNet®

mantra
     n 1: a commonly repeated word or phrase; "she repeated `So
          pleased with how its going' at intervals like a mantra"
     2: (Sanskrit) literally a `sacred utterance' in Vedism; one of
        a collection of orally transmitted poetic hymns