all clear vs permission

all clear and permission both are nouns.

Word	Noun	Adjective	Verb	Adverb
all clear	Yes	No	No	No
permission	Yes	No	No	No

As nouns, permission is a hypernym of all clear; that is, permission is a word with a broader meaning than all clear:

all clear (noun)	permission (noun)
a signal (usually a siren) that danger is over	the act of giving a formal (usually written) authorization
permission to proceed because obstacles have been removed	approval to do something