The Collaborative International Dictionary of English v.0.48:

Probationary \Pro*ba"tion*a*ry\, a.
   Of or pertaining to probation; serving for trial.
   [1913 Webster]

         To consider this life . . . as a probationary state.
                                                  --Paley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

probationary
    adj 1: under terms not final or fully worked out or agreed upon;
           "probationary employees"; "a provisional government";
           "just a tentative schedule" [syn: probationary,
           provisional, provisionary, tentative]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "probationary":
   cut-and-try, empirical, experimental, heuristic, hit-or-miss,
   on probation, pilot, probational, probative, probatory, proving,
   provisional, tentative, test, testing, trial, trial-and-error,
   trying, verificatory