Dictionary.com/ingenue (etymology):

ingénue also ingenue (AN-zhuh-noo) noun

1. A naive, innocent girl or young woman.
2. 1. The role of an ingénue in a dramatic production.
   2. An actress playing such a role.

Source: The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2000 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.

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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.

Source: Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.

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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

Source: WordNet ® 2.0, © 2003 Princeton University