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]