The Collaborative International Dictionary of English v.0.48:

Controversial \Con`tro*ver"sial\, a. [Cf. LL. controversialis.]
   Relating to, or consisting of, controversy; disputatious;
   polemical; as, controversial divinity.
   [1913 Webster]

         Whole libraries of controversial books.  --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

controversial
    adj 1: marked by or capable of arousing controversy; "the issue
           of the death penalty is highly controversial"; "Rushdie's
           controversial book"; "a controversial decision on
           affirmative action" [ant: noncontroversial,
           uncontroversial]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "controversial":
   arguable, argumental, argumentative, at issue, belligerent,
   cat-and-dog, cat-and-doggish, combative, confutable, conjectural,
   contentious, contestable, controvertible, debatable, deniable,
   dialectic, disputable, disputatious, doubtable, doubtful, dubious,
   dubitable, eristic, factious, iffy, ill-humored, in dispute,
   in doubt, in dubio, in question, litigious, logomachic, mistakable,
   moot, open to doubt, open to question, pilpulistic, polemic,
   polemical, pro and con, problematic, provocative, quarrelsome,
   questionable, refutable, scrappy, speculative, suppositional,
   suspect, suspicious, unsettled