cashbox vs strongbox

cashbox and strongbox both are nouns.

Word	Noun	Adjective	Verb	Adverb
cashbox	Yes	No	No	No
strongbox	Yes	No	No	No

As nouns, strongbox is a hypernym of cashbox; that is, strongbox is a word with a broader meaning than cashbox:

cashbox: a strongbox for holding cash
strongbox: a strongly made box for holding money or valuables; can be locked

Other hypernyms of cashbox include deedbox.

cashbox (noun)	strongbox (noun)
a strongbox for holding cash	a strongly made box for holding money or valuables; can be locked