sandbag vs strengthen

sandbag is a noun but strengthen is not a noun.

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

As verbs, strengthen is a hypernym of sandbag; that is, strengthen is a word with a broader meaning than sandbag:

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

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