prehension vs clench

prehension and clench both are nouns.

Word	Noun	Adjective	Verb	Adverb
prehension	Yes	No	No	No
clench	Yes	No	Yes	No

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

prehension: the act of gripping something firmly with the hands (or the tentacles)
clench: the act of grasping

Other hyponyms of prehension include clasp, clutch, clutches, grasp, grip, hold.

prehension (noun)	clench (noun)
the act of gripping something firmly with the hands (or the tentacles)	the act of grasping
	a small slip noose made with seizing

prehension (verb)	clench (verb)
	hold in a tight grasp
	squeeze together tightly