Source : Webster's Revised Unabridged Dictionary (1913)

Thalia \Tha*li"a\, n. [L., fr. Gr. Qa`leia, originally,
   blooming, luxuriant, akin to qa`llein to be luxuriant.]
   (Class. Myth.)
   (a) That one of the nine Muses who presided over comedy.
   (b) One of the three Graces.
   (c) One of the Nereids.

Source : WordNet®

Thalia
     n 1: (Greek mythology) the Muse of comedy and pastoral poetry
     2: (Greek mythology) one of the three Graces