ret·ro·flex 
(rĕtrə-flĕks′)
(rĕtrə-flĕks′)adj. also ret·ro·flexed (-flĕkst′)
1. Bent, curved, or turned backward.
2. Pronounced with the tip of the tongue turned back against the roof of the mouth.
n.
A sound pronounced with the tongue in retroflex position, as the sound (r) in some varieties of English.
[Latin *retrōflexus, past participle of retrōflectere, to bend back : retrō, retro- + flectere, to bend.]
ret′ro·flexion, ret′ro·flection n.