leave alone vs let

leave alone is not a noun while let is a noun.

Word	Noun	Adjective	Verb	Adverb
leave alone	No	No	Yes	No
let	Yes	No	Yes	No

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

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

leave alone (verb)	let (verb)
leave unchanged or undisturbed or refrain from taking	leave unchanged
	cause to move; cause to be in a certain position or condition
	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