The Collaborative International Dictionary of English v.0.48:

Retroflexion \Re`tro*flex"ion\, n.
   The act of reflexing; the state of being retroflexed. Cf.
   Retroversion.
   [1913 Webster] Retrofract

WordNet (r) 3.0 (2006):

retroflexion
    n 1: a turning or tilting backward of an organ or body part;
         "retroversion of the uterus" [syn: retroversion,
         retroflection, retroflexion]
    2: an articulatory gesture made by turning the tip of the tongue
       back against the roof of the mouth [syn: retroflection,
       retroflexion]
    3: the act of bending backward [syn: retroflection,
       retroflexion]