departure vs flexion

departure and flexion both are nouns.

Word	Noun	Adjective	Verb	Adverb
departure	Yes	No	No	No
flexion	Yes	No	No	No

As nouns, flexion is a hyponym of departure; that is, flexion is a word with a more specific, narrower meaning than departure:

Other hyponyms of departure include discrepancy, variance, variant, driftage, flection, inflection.

departure (noun)	flexion (noun)
the act of departing	act of bending a joint; especially a joint between the bones of a limb so that the angle between them is decreased
euphemistic expressions for death	deviation from a straight or normal course
a variation that deviates from the standard or norm	the state of being flexed (as of a joint)