The Collaborative International Dictionary of English v.0.48:

Probationer \Pro*ba"tion*er\, n.
   [1913 Webster]
   1. One who is undergoing probation; one who is on trial; a
      novice.
      [1913 Webster]

            While yet a young probationer,
            And candidate of heaven.              --Dryden.
      [1913 Webster]

   2. A student in divinity, who, having received certificates
      of good morals and qualifications from his university, is
      admitted to several trials by a presbytery, and, on
      acquitting himself well, is licensed to preach. [Scot.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

probationer
    n 1: a nurse in training who is undergoing a trial period [syn:
         probationer, student nurse]
    2: someone released on probation or on parole [syn:
       probationer, parolee]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "probationer":
   LPN, RN, abecedarian, alphabetarian, apprentice, articled clerk,
   baby, beginner, boot, catechumen, charge nurse, deb, debutant,
   district nurse, entrant, fledgling, freshman, graduate nurse,
   greenhorn, greeny, ignoramus, inductee, infant, initiate, learner,
   licensed practical nurse, neophyte, nestling, new boy, newcomer,
   novice, novitiate, nurse, nursing sister, postulant,
   practical nurse, private-duty nurse, probationist, probe,
   public health nurse, raw recruit, recruit, registered nurse,
   rookie, school nurse, scrub nurse, sister, student nurse,
   surgical nurse, tenderfoot, trained nurse, trainee, tyro,
   visiting nurse