passkey vs skeleton key

passkey and skeleton key both are nouns.

Word	Noun	Adjective	Verb	Adverb
passkey	Yes	No	No	No
skeleton key	Yes	No	No	No

As nouns, skeleton key is a hyponym of passkey; that is, skeleton key is a word with a more specific, narrower meaning than passkey:

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

passkey (noun)	skeleton key (noun)
key that secures entrance everywhere	a passkey with much of the bit filed away so that it can open different locks