The Collaborative International Dictionary of English v.0.48:

Diva \Di"va\ (d[=e]"v[.a]), n.; It. pl. Dive (d[=e]"v[=a]).
   [It., prop. fem. of divo divine, L. divus.]
   A prima donna.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

diva
    n 1: a distinguished female operatic singer; a female operatic
         star [syn: prima donna, diva]

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "diva":
   Heldentenor, Meistersinger, alto, aria singer, baritenor, baritone,
   bass, basso, basso buffo, basso cantante, basso profundo,
   blues singer, canary, cantatrice, cantor, caroler, chanter,
   chantress, coloratura soprano, comic bass, contralto, countertenor,
   crooner, danseur noble, deep bass, dramatic soprano,
   feature attraction, first tragedian, headliner, heavy lead, hero,
   heroic tenor, heroine, hymner, improvisator, jeune premier, lead,
   lead singer, leading lady, leading man, lieder singer, melodist,
   mezzo-soprano, opera singer, prima ballerina, prima donna,
   principal, protagonist, psalm singer, rock-and-roll singer, singer,
   singstress, songbird, songster, songstress, soprano, star,
   superstar, tenor, torch singer, vocalist, vocalizer, voice,
   warbler, yodeler