The Collaborative International Dictionary of English v.0.48:

Experimental \Ex*per`i*men"tal\, a. [Cf.F. exp['e]rimental.]
   1. Pertaining to experiment; founded on, or derived from,
      experiment or trial; as, experimental science; given to,
      or skilled in, experiment; as, an experimental
      philosopher.
      [1913 Webster]

   2. Known by, or derived from, experience; as, experimental
      religion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

experimental
    adj 1: relating to or based on experiment; "experimental
           physics"
    2: relying on observation or experiment; "experimental results
       that supported the hypothesis" [syn: experimental, data-
       based, observational]
    3: of the nature of or undergoing an experiment; "an
       experimental drug"

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "experimental":
   conjectural, cut-and-try, determined, developmental, empirical,
   experiential, exploratory, heuristic, hit-or-miss, hypothetical,
   pilot, preliminary, preparatory, probationary, probative,
   probatory, proving, provisional, resolute, speculative, temporary,
   tentative, test, testing, theoretical, trial, trial-and-error,
   trying, venturesome, verificatory, willing