stiffen vs trammel

stiffen is not a noun while trammel is a noun.

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

As verbs, trammel is a hypernym of stiffen; that is, trammel is a word with a broader meaning than stiffen:

Other hypernyms of stiffen include bound, confine, limit, restrict, throttle.

stiffen (noun)	trammel (noun)
	a restraint that confines or restricts freedom (especially something used to tie down or restrain a prisoner)
	a restraint that is used to teach a horse to amble
	an adjustable pothook set in a fireplace
	a fishing net with three layers; the outer two are coarse mesh and the loose inner layer is fine mesh

stiffen (verb)	trammel (verb)
become stiff or stiffer	place limits on (extent or amount or access)
make stiff or stiffer	catch in or as if in a trap
severely restrict in scope or extent