stiffen vs starch

stiffen is not a noun while starch is a noun.

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

As verbs, starch is a hyponym of stiffen; that is, starch is a word with a more specific, narrower meaning than stiffen:

Other hyponyms of stiffen include buckram, ossify, petrify, rigidify.

stiffen (noun)	starch (noun)
	a complex carbohydrate found chiefly in seeds, fruits, tubers, roots and stem pith of plants, notably in corn, potatoes, wheat, and rice; an important foodstuff and used otherwise especially in adhesives and as fillers and stiffeners for paper and textiles
	a commercial preparation of starch that is used to stiffen textile fabrics in laundering

stiffen (verb)	starch (verb)
become stiff or stiffer	stiffen with starch
make stiff or stiffer
severely restrict in scope or extent