WordNet (r) 3.0 (2006):

scriptwriter
    n 1: someone who writes scripts for plays or movies or broadcast
         dramas

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "scriptwriter":
   advertising writer, annalist, art critic, author, authoress,
   belletrist, bibliographer, choreographer, coauthor, collaborator,
   columnist, comedian, compiler, composer, copywriter,
   creative writer, critic, dance critic, diarist, drama critic,
   dramatist, dramatizer, dramaturge, encyclopedist, essayist, farcer,
   farceur, farceuse, farcist, free lance, free-lance writer, gagman,
   ghost, ghostwriter, humorist, inditer, joke writer, jokesmith,
   librettist, literary artist, literary craftsman, literary critic,
   literary man, litterateur, logographer, magazine writer,
   man of letters, melodramatist, mimographer, monodramatist,
   monographer, music critic, newspaperman, novelettist, novelist,
   pamphleteer, penwoman, play doctor, play fixer, playwright,
   playwriter, poet, prose writer, reviewer, scenario writer,
   scenarioist, scenarist, scribe, short-story writer, storyteller,
   technical writer, tragedian, word painter, wordsmith, writer