let vs leave alone

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

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

As verbs, leave alone is a hypernym of let; that is, leave alone is a word with a broader meaning than let:

Other hypernyms of let include leave, leave behind, let alone.

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

let (verb)	leave alone (verb)
leave unchanged	leave unchanged or undisturbed or refrain from taking
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