The Collaborative International Dictionary of English v.0.48:
Retrorse \Re*trorse"\, a. [L. retrorsus, retroversus; retro back + vertere, versum, to turn. Cf. Retrovert.] Bent backward or downward. -- Re*trorse"ly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
retrorse adj 1: bent or curved backward or downward; "leaves with retrorse barbs" [ant: antrorse]