The Collaborative International Dictionary of English v.0.48:

Climactic \Cli*mac"tic\, a.
   Of or pertaining to a climax; forming, or of the nature of, a
   climax, or ascending series.

         A fourth kind of parallelism . . . is still
         sufficiently marked to be noticed by the side of those
         described by Lowth, viz., climactic parallelism
         (sometimes called "ascending rhythm").   --S. R.
                                                  Driver.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

climactic
    adj 1: consisting of or causing a climax; "a climactic
           development" [ant: anticlimactic]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "climactic":
   acmatic, apical, capital, chief, consummate, head, headmost,
   highest, maximal, maximum, meridian, meridional, overmost,
   paramount, preeminent, summital, supreme, tip-top, top, topmost,
   ultimate, upmost, uppermost, vertical, zenithal