Source : Webster's Revised Unabridged Dictionary (1913)

Retrorse \Re*trorse"\, a. [L. retrorsus, retroversus; retro back
   + vertere, versum, to turn. Cf. {Retrovert}.]
   Bent backward or downward. -- {Re*trorse"ly}, adv.

Source : WordNet®

retrorse
     adj : bent or curved backward or downward; "leaves with retrorse
           barbs" [ant: {antrorse}]