Webster's Revised Unabridged Dictionary · 1913

Flexion

Flexion , noun

[Latin flexio: compare French flexion.]

1.
The act of flexing or bending; a turning.
2.
A bending; a part bent; a fold. — Bacon
3.
(Grammar) Syntactical change of form of words, as by declension or conjugation; inflection.
Express the syntactical relations by flexion. — Sir W. Hamilton
4.
(Physiology) 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.