let vs authorise

let is a noun but authorise is not a noun.

Word	Noun	Adjective	Verb	Adverb
let	Yes	No	Yes	No
authorise	No	No	Yes	No

As verbs, authorise is a hyponym of let; that is, authorise is a word with a more specific, narrower meaning than let:

let (noun)	authorise (noun)
a serve that strikes the net before falling into the receiver's court; the ball must be served again

let (verb)	authorise (verb)
leave unchanged	grant authorization or clearance for
cause to move; cause to be in a certain position or condition	give or delegate power or authority to
actively cause something to happen
consent to, give permission; permit
grant use or occupation of under a term of contract
make it possible through a specific action or lack of action for something to happen