1.ConjunctionMuch less; to say nothing of; used after one negative clause to introduce another, usually broader and more important clause, whose negation is implied by the negation of the first. However either of these instances mentioned can be applied with the use of let alone.
"He couldn't boil water, let alone prepare a dinner for eight."
2.ConjunctionNot to mention, as well as; used after one item, to introduce a further item which is entailed by the first.
3.VerbTo leave alone, let be; to stop bothering.
"I wish he would let me alone so I could get some sleep."