strengthen vs sandbag

strengthen is not a noun while sandbag is a noun.

Word	Noun	Adjective	Verb	Adverb
strengthen	No	No	Yes	No
sandbag	Yes	No	Yes	No

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

Other hyponyms of strengthen include consolidate, proof, back, toughen.

strengthen (noun)	sandbag (noun)
	a bag filled with sand; used as a weapon or to build walls or as ballast

strengthen (verb)	sandbag (verb)
give a healthy elasticity to	protect or strengthen with sandbags; stop up
gain strength	downplay one's ability (towards others) in a game in order to deceive, as in gambling
make strong or stronger	hit something or somebody as if with a sandbag
	treat harshly or unfairly
	compel by coercion, threats, or crude means