The Collaborative International Dictionary of English v.0.48:

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.
       [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "Thalia":
   Calliope, Clio, Erato, Euterpe, Melpomene, Polyhymnia, Terpsichore,
   arlequinade, artistic imagination, black comedy, broad comedy,
   burlesque, burletta, camp, comedie bouffe, comedie larmoyante,
   comedie rosse, comedietta, comedy, comedy ballet, comedy of humors,
   comedy of ideas, comedy of intrigue, comedy of manners,
   comedy of situation, comedy relief, comic muse, comic opera,
   comic relief, conception, creative imagination, creative power,
   creative thought, dark comedy, domestic comedy,
   esemplastic imagination, esemplastic power, exode, farce,
   farce comedy, genius, genteel comedy, harlequinade, high camp,
   inspiration, light comedy, low camp, low comedy, mime, muse,
   musical, musical comedy, mythicization, mythification, mythopoeia,
   opera buffa, poetic imagination, raw comedy, realistic comedy,
   romantic comedy, satyr play, sentimental comedy,
   shaping imagination, situation comedy, slapstick, slapstick comedy,
   tragicomedy