constrain vs stiffen

constrain and stiffen both are verbs.

Word	Noun	Adjective	Verb	Adverb
constrain	No	No	Yes	No
stiffen	No	No	Yes	No

As verbs, constrain and stiffen are synonyms defined as:

Other synonyms of constrain include tighten, tighten up.

constrain (verb)	stiffen (verb)
severely restrict in scope or extent	become stiff or stiffer
to close within bounds, or otherwise limit or deprive of free movement	make stiff or stiffer
compel to behave in a certain way	severely restrict in scope or extent