WordNet (r) 3.0 (2006):

trainee
    n 1: someone who is being trained

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "trainee":
   apprentice, auditor, autodidact, baby, beginner, boot, catechumen,
   conscript, deb, debutant, draft, drafted man, draftee, educatee,
   enlistee, enrollee, entrant, fledgling, freshman, greenhorn,
   greeny, inductee, infant, inquirer, learner, levy, monitor,
   neophyte, nestling, newcomer, novice, novitiate, praepostor,
   prefect, probationer, pupil, raw recruit, recruit, rookie, scholar,
   selectee, self-taught person, student, studier, tenderfoot, tyro