NOUN (2)

1. a commonly repeated word or phrase;
- Example: "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;

The Collaborative International Dictionary of English v.0.48:

Mantra \Man"tra\, n. [Skr.]
   A prayer; an invocation; a religious formula; a charm.
   [India]
   [1913 Webster]

   Note: Among the Hindoos each caste and tribe has a mantra
         peculiar to itself; as, the mantra of the Brahmans.
         --Balfour (Cyc. of India).
         [1913 Webster]

WordNet (r) 3.0 (2006):

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