starch vs stiffen

starch is a noun but stiffen is not a noun.

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

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

starch (noun)	stiffen (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

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