The Collaborative International Dictionary of English v.0.48:

Ironic \I*ron"ic\, a.
   Ironical. --Sir T. Herbert.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ironic
    adj 1: humorously sarcastic or mocking; "dry humor"; "an ironic
           remark often conveys an intended meaning obliquely"; "an
           ironic novel"; "an ironical smile"; "with a wry Scottish
           wit" [syn: dry, ironic, ironical, wry]
    2: characterized by often poignant difference or incongruity
       between what is expected and what actually is; "madness, an
       ironic fate for such a clear thinker"; "it was ironical that
       the well-planned scheme failed so completely" [syn: ironic,
       ironical]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "ironic":
   Rabelaisian, allusive, allusory, amalgamated, ambiguous,
   ambivalent, amphibious, amphibological, amphibolous, antinomic,
   biting, blended, caustic, combined, complex, composite, compound,
   compounded, conglomerate, cutting, cynical, dappled, dry, eclectic,
   enigmatic, equivocal, equivocatory, fifty-fifty, half-and-half,
   heterogeneous, implicational, implicative, implicatory, incisive,
   indicative, indiscriminate, inferential, insinuating, insinuative,
   insinuatory, intricate, jumbled, many-sided, medley, mingled,
   miscellaneous, mixed, mordant, motley, multifaceted, multinational,
   multiracial, multivocal, mysterious, obscure, oxymoronic,
   paradoxical, patchy, pluralistic, polysemantic, polysemous,
   promiscuous, referential, sarcastic, sardonic, satiric, scathing,
   scrambled, self-contradictory, suggestive, syncretic,
   thrown together, trenchant, uncertain, varied, wry