let vs let alone

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

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

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

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

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

let (verb)	let 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

let (adverb)	let alone (adverb)
	much less