The Collaborative International Dictionary of English v.0.48:

Heroine \Her"o*ine\, n. [F. h['e]ro["i]ne, L. heroina, Gr. ?,
   fem. of ?. See Hero.]
   1. A woman of an heroic spirit.
      [1913 Webster]

            The heroine assumed the woman's place. --Dryden.
      [1913 Webster]

   2. The principal female person who figures in a remarkable
      action, or as the subject of a poem or story.
      [1913 Webster]

WordNet (r) 3.0 (2006):

heroine
    n 1: the main good female character in a work of fiction
    2: a woman possessing heroic qualities or a woman who has
       performed heroic deeds

Moby Thesaurus II by Grady Ward, 1.0:

104 Moby Thesaurus words for "heroine":
   Achilles, David, Hector, Roland, Samson, a man, actor, antagonist,
   antihero, big name, bit, bit part, brave, bulldog, cast, celebrity,
   character, chutzpanik, constellation, cue, cynosure, danseur noble,
   decorated hero, demigod, demigoddess, diva, fat part,
   feature attraction, feeder, fighting cock, figure, first tragedian,
   folk hero, galaxy, gallant, gamecock, god, goddess, godkin, godlet,
   godling, good soldier, great man, headliner, heavy, heavy lead,
   hero, idol, immortal, important person, ingenue, jeune premier,
   lead, lead role, leading lady, leading man, leading woman, lines,
   lion, luminaries, luminary, man of courage, man of mark,
   master spirit, name, notability, notable, paladin, part, person,
   person of note, personage, phoenix, piece, pleiad, pop hero,
   popular hero, popular idol, prima ballerina, prima donna,
   principal, protagonist, public figure, role, side, singer,
   social lion, somebody, soubrette, stalwart, star, straight part,
   superstar, supporting character, supporting role, the brave, tiger,
   title role, valiant, valiant knight, villain, walk-on,
   walking part, worthy