The Collaborative International Dictionary of English v.0.48:

Retroflex \Re"tro*flex\, Retroflexed \Re"tro*flexed\, a. [Pref.
   retro- + L. flectere, flexum, to bend, to turn.]
   Reflexed; bent or turned abruptly backward.
   [1913 Webster]

WordNet (r) 3.0 (2006):

retroflex
    adj 1: bent or curved backward [syn: retroflex, retroflexed]
    2: pronounced with the tip of the tongue turned back toward the
       hard palate [syn: cacuminal, retroflex]
    v 1: bend or turn backward [syn: retroflex, replicate]
    2: articulate (a consonant) with the tongue curled back against
       the palate; "Indian accents can be characterized by the fact
       that speakers retroflex their consonants"

Moby Thesaurus II by Grady Ward, 1.0:

175 Moby Thesaurus words for "retroflex":
   accented, allophone, alveolar, apical, apico-alveolar,
   apico-dental, arch, articulated, articulation, aspiration,
   assimilated, assimilation, back, backslide, barytone, bend,
   bend back, bilabial, bow, broad, cacuminal, central, cerebral,
   check, checked, close, cock, consonant, consonantal, continuant,
   crook, curl, curve, decurve, deflect, dental, diphthong,
   dissimilated, dissimilation, dome, dorsal, embow, epenthetic vowel,
   explosive, fall astern, fall behind, flat, flex, front, get behind,
   glide, glossal, glottal, glottalization, go backwards, go behind,
   guttural, hard, heavy, high, hook, hump, hunch, incurvate, incurve,
   inflect, intonated, jerk back, labial, labialization, labiodental,
   labiovelar, lapse, laryngeal, lateral, lax, light, lingual, liquid,
   loop, lose ground, low, manner of articulation, mid, modification,
   monophthong, monophthongal, morphophoneme, mute, muted, narrow,
   nasal, nasalized, occlusive, open, oxytone, palatal, palatalized,
   parasitic vowel, peak, pharyngeal, pharyngealization,
   pharyngealized, phone, phoneme, phonemic, phonetic, phonic, pitch,
   pitched, plosive, posttonic, prothetic vowel, pull back, recede,
   recidivate, recurve, reflect, reflex, regress, relapse, retrocede,
   retrograde, retrogress, return, revert, round, rounded, sag,
   segmental phoneme, semivowel, slip back, soft, sonant, sonority,
   speech sound, stop, stopped, stressed, strong, surd, swag, sweep,
   syllabic, syllabic nucleus, syllabic peak, syllable, tense, thick,
   throaty, tonal, tonic, transition sound, triphthong, turn, twangy,
   unaccented, unrounded, unstressed, vault, velar, vocable, vocalic,
   vocoid, voice, voiced, voiced sound, voiceless, voiceless sound,
   voicing, vowel, vowellike, weak, wide, wind