safety-deposit vs strongbox

safety-deposit and strongbox both are nouns.

Word	Noun	Adjective	Verb	Adverb
safety-deposit	Yes	No	No	No
strongbox	Yes	No	No	No

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

safety-deposit: a fireproof metal strongbox (usually in a bank) for storing valuables
strongbox: a strongly made box for holding money or valuables; can be locked

Other hypernyms of safety-deposit include deedbox.

safety-deposit (noun)	strongbox (noun)
a fireproof metal strongbox (usually in a bank) for storing valuables	a strongly made box for holding money or valuables; can be locked