flexion (n.)

c. 1600, "bent part," also, in grammar, "modification of part of a word," from Latin flexionem (nominative flexio) "a bending, swaying; bend, turn, curve," noun of action from past participle stem of flectere "to bend" (see flexible). Flection (18c.) is more recent, less etymological, but said to be more common in modern English, perhaps by influence of affection, direction, where the -ct- is in the Latin word. According to some modern dictionaries, flexion is "confined to anatomical contexts." Related: Flexional; flectional.