The Collaborative International Dictionary of English v.0.48:

Contraindication \Con"tra*in`di*ca"tion\, n. (med.)
   An indication or symptom which forbids the method of
   treatment usual in such cases.
   [1913 Webster]

WordNet (r) 3.0 (2006):

contraindication
    n 1: (medicine) a reason that makes it inadvisable to prescribe
         a particular drug or employ a particular procedure or
         treatment [ant: indication]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "contraindication":
   antagonism, antipathy, antithesis, clashing, collision, conflict,
   confrontation, contradiction, contradistinction, contraposition,
   contrariety, contrast, counterposition, cross-purposes,
   disagreement, discrepancy, hostility, inconsistency, inimicalness,
   oppositeness, opposition, opposure, oppugnance, oppugnancy,
   perversity, polarity, repugnance, showdown