license vs clearance

license and clearance both are nouns.

Word	Noun	Adjective	Verb	Adverb
license	Yes	No	Yes	No
clearance	Yes	No	No	No

As nouns, clearance is a hyponym of license; that is, clearance is a word with a more specific, narrower meaning than license:

Other hyponyms of license include conge, congee, allowance, dispensation, toleration.

license (noun)	clearance (noun)
the act of giving a formal (usually written) authorization	permission to proceed
a legal document giving official permission to do something	the distance by which one thing clears another; the space between them
freedom to deviate deliberately from normally applicable rules or practices (especially in behavior or speech)	vertical space available to allow easy passage under something
excessive freedom; lack of due restraint

license (verb)	clearance (verb)
authorize officially