- (idiomatic, negative polarity item) Much 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.
- He couldn't boil water, let alone prepare a dinner for eight.
- (idiomatic, positive polarity item, rare) not to mention, as well as; used after one item, to introduce a further item which is entailed by the first.
- Sometimes used with the order of items reversed.
(third-person singular simple present lets alone, present participle letting alone, simple past and past participle let alone)
- To leave alone, let be; to stop bothering.
- I wish he would let me alone so I could get some sleep.