1.  flexion(n = noun.state) flection, flexure - the state of being flexed (as of a joint);
is a kind of physical condition, physiological condition, physiological state

2.  flexion(n = noun.event) flection, inflection - deviation from a straight or normal course;
is a kind of departure, deviation, difference, divergence

3.  flexion(n = noun.act) flexure - act of bending a joint; especially a joint between the bones of a limb so that the angle between them is decreased;
is a kind of bending
has particulars: flex, dorsiflexion
Antonym: extension

1.  The act of flexing or bending; a turning. [1913 Webster]

2.  A bending; a part bent; a fold. Bacon. [1913 Webster]

3.  Syntactical change of form of words, as by declension or conjugation; inflection. [1913 Webster]
"Express the syntactical relations by flexion." [1913 Webster]

4.  The bending of a limb or joint; that motion of a joint which gives the distal member a continually decreasing angle with the axis of the proximal part; -- distinguished from extension. [1913 Webster]

flexion, n. (US flection)
1 a the act of bending or the condition of being bent, esp. of a limb or joint. b a bent part; a curve.
2 Gram. inflection.
3 Math. = FLEXURE.

Derivative:
flexional adj. (in sense 2). flexionless adj. (in sense 2).

Etymology:
L flexio (as FLEX(1))

N  curvature, curvity, curvation, incurvature, incurvity, incurvation, bend, flexure, flexion, flection, conflexure, crook, hook, bought, bending, deflection, deflexion, inflection, inflexion, concameration, arcuation, devexity, turn, deviation, detour, sweep, curl, curling, bough, recurvity, recurvation, sinuosity, kink, carve, arc, arch, arcade, vault, bow, crescent, half-moon, lunule, horseshoe, loop, crane neck, parabola, hyperbola, helix, spiral, catenary, festoon, conchoid, cardioid, caustic, tracery, arched ceiling, arched roof, bay window, bow window, sine curve, spline, spline curve, spline function, obliquity, curved, curviform, curvilineal, curvilinear, devex, devious, recurved, recurvous, crump, bowed, vaulted, hooked, falciform, falcated, semicircular, crescentic, sinusoid, parabolic, paraboloid, luniform, lunular, semilunar, conchoidal, helical, double helical, spiral, kinky, cordiform, cordated, cardioid, heart shaped, bell shaped, boat shaped, crescent shaped, lens shaped, moon shaped, oar shaped, shield shaped, sickle shaped, tongue shaped, pear shaped, fig shaped, kidney-shaped, reniform, lentiform, lenticular, bow-legged, oblique, circular, aduncated, arclike, arcuate, arched, beaked, bicorn, bicornuous, bicornute, clypeate, clypeiform, cymbiform, embowed, galeiform, hamate, hamiform, hamous, hooked, linguiform, lingulate, lobiform, lunate, navicular, peltate, remiform, rhamphoid, rostrate, rostriferous, rostroid, scutate, scaphoid, uncate, unguiculate, unguiform.

N  fold, plicature, plait, pleat, ply, crease, tuck, gather, flexion, flexure, joint, elbow, double, doubling, duplicature, gather, wrinkle, rimple, crinkle, crankle, crumple, rumple, rivel, ruck, ruffle, dog's ear, corrugation, frounce, flounce, lapel, pucker, crow's feet, plication, folded, fluted, pleated.

N  deviation, swerving, obliquation, warp, refraction, flection, flexion, sweep, deflection, deflexure, declination, diversion, digression, depart from, aberration, divergence, zigzag, detour, divagation, wandering, vagrancy, evagation, bypaths and crooked ways, byroad, sidling, knight's move at chess, deviating, aberrant, errant, excursive, discursive, devious, desultory, loose, rambling, stray, erratic, vagrant, undirected, circuitous, indirect, zigzag, crab-like, astray from, round about, wide of the mark, to the right about, all manner of ways, circuitously, obliquely, sideling, like the move of the knight on a chessboard.