NOUN (3)

1. an actress who specializes in playing the role of an artless innocent young girl;

2. an artless innocent young girl (especially as portrayed on the stage);

3. the role of an innocent artless young woman in a play;

The Collaborative International Dictionary of English v.0.48:

Ing'enue \In`g['e]`nue"\ ([a^]N`zh[asl]`n[.u]"), n.; pl.
   -nues. [F., fem. of ing['e]nu ingenious.]
   An ingenuous or na["i]ve girl or young woman, or an actress
   representing such a person.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

ingenue
    n 1: an actress who specializes in playing the role of an
         artless innocent young girl
    2: an artless innocent young girl (especially as portrayed on
       the stage)
    3: the role of an innocent artless young woman in a play

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "ingenue":
   Roscius, actor, actress, antagonist, antihero, babe, bad guy,
   barnstormer, bit, bit part, cast, character, character actor,
   character man, character woman, child, child actor,
   child of nature, cue, diseur, diseuse, dove, dramatizer, dupe,
   fat part, feeder, foil, heavy, hero, heroine, hick, histrio,
   histrion, infant, innocent, juvenile, lamb, lead, lead role,
   leading lady, leading man, leading woman, lines, lout,
   matinee idol, mere child, mime, mimer, mimic, monologist, mummer,
   noble savage, oaf, pantomime, pantomimist, part, person, personage,
   piece, playactor, player, protagonist, protean actor, reciter,
   role, rube, side, simple soul, soubrette, stage performer,
   stage player, stooge, straight man, straight part, stroller,
   strolling player, supporting character, supporting role,
   theatrical, thespian, title role, trouper, unsophisticate,
   utility man, villain, walk-on, walking part, yokel