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]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "retroflexion":
   backset, backsliding, backward motion, backward step, ectropion,
   eversion, introversion, intussusception, invagination, inversion,
   lapse, pronation, reaction, recession, recidivation, recidivism,
   reentry, refluence, reflux, regress, regression, relapse,
   resupination, retroaction, retrocession, retrogradation,
   retrogression, retroversion, retrusion, return, reversal,
   reversing, reversion, revulsion, rollback, setback, sternway,
   supination, throwback, topsy-turviness, topsy-turvydom, transposal,
   transposition, turning back, turning backwards, turning inside out,
   turning inward, turning over