skeleton key vs passe-partout

skeleton key and passe-partout both are nouns.

Word	Noun	Adjective	Verb	Adverb
skeleton key	Yes	No	No	No
passe-partout	Yes	No	No	No

As nouns, passe-partout is a hypernym of skeleton key; that is, passe-partout is a word with a broader meaning than skeleton key:

skeleton key: a passkey with much of the bit filed away so that it can open different locks
passe-partout: key that secures entrance everywhere

Other hypernyms of skeleton key include master, master key, passkey.

skeleton key (noun)	passe-partout (noun)
a passkey with much of the bit filed away so that it can open different locks	key that secures entrance everywhere
	a mounting for a picture using gummed tape