The Collaborative International Dictionary of English v.0.48:

Vocalist \Vo"cal*ist\, n. [Cf. F. vocaliste.]
   A singer, or vocal musician, as opposed to an
   instrumentalist.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vocalist
    n 1: a person who sings [syn: singer, vocalist, vocalizer,
         vocaliser]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "vocalist":
   Heldentenor, Meistersinger, alto, aria singer, baritenor, baritone,
   bass, basso, basso buffo, basso cantante, basso profundo,
   blues singer, canary, cantatrice, cantor, caroler, chanter,
   chantress, choir member, choirboy, chorister, chorus girl,
   coloratura soprano, comic bass, contralto, countertenor, crooner,
   deep bass, diva, dramatic soprano, heroic tenor, hymner,
   improvisator, lead singer, lieder singer, melodist, mezzo-soprano,
   nightingale, opera singer, prima donna, psalm singer,
   rock-and-roll singer, singer, singstress, soloist, songbird,
   songster, songstress, soprano, tenor, thrush, torch singer,
   vocalizer, voice, warbler, yodeler