The Collaborative International Dictionary of English v.0.48:

Soprano \So*pra"no\, n.; pl. E. Sopranos, It. Soprani. [It.,
   fr. soprano superior, highest, fr. sopra above, L. supra. See
   Sovereign.] (Mus.)
   (a) The treble; the highest vocal register; the highest kind
       of female or boy's voice; the upper part in harmony for
       mixed voices.
   (b) A singer, commonly a woman, with a treble voice.
       [1913 Webster]

WordNet (r) 3.0 (2006):

soprano
    adj 1: having or denoting a high range; "soprano voice";
           "soprano sax"; "the boy still had a fine treble voice";
           "the treble clef" [syn: soprano, treble]
    n 1: a female singer
    2: the highest female voice; the voice of a boy before puberty
    3: the pitch range of the highest female voice [syn: soprano,
       treble]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "soprano":
   Heldentenor, Meistersinger, accompaniment, alto, aria singer,
   baritenor, baritone, bass, basso, basso buffo, basso cantante,
   basso continuo, basso ostinato, basso profundo, bassus,
   blues singer, bravura, canary, cantatrice, canto, cantor, cantus,
   cantus figuratus, cantus planus, caroler, chanter, chantress,
   choral, choric, coloratura, coloratura soprano, comic bass,
   continuo, contralto, countertenor, crooner, deep bass, descant,
   diva, dramatic, dramatic soprano, drone, falsetto, figured bass,
   ground bass, head register, head tone, head voice, heroic,
   heroic tenor, high, high-pitched, high-sounding, high-toned,
   hymnal, hymner, improvisator, lead singer, lieder singer, line,
   liturgical, lyric, male alto, melodist, mezzo-soprano,
   opera singer, operatic, part, plain chant, plain song, prick song,
   prima donna, psalm singer, psalmic, psalmodial, psalmodic,
   rock-and-roll singer, sacred, singer, singing, singstress,
   songbird, songster, songstress, tenor, thorough bass, torch singer,
   treble, undersong, vocal, vocalist, vocalizer, voice, voice part,
   warbler, yodeler