From Longman Dictionary of Contemporary Englishlet alonelet aloneIMPOSSIBLEused after a negative statement to say that the next thing you mention is even more unlikely The baby can’t even sit up yet, let alone walk! → let
Examples from the Corpus
let alone• Hardly an inspirational notion, let alone a formula for improved customer relations.• It's unwise to let policy be influenced, let alone jeopardized, by outraged personal pride.• If your income drops or ends, how will you pay them off, let alone keep up with the accumulating interest?• I doubt he would have given one of his grandparents a point that morning, let alone me.• I wouldn't work with my mom, let alone my whole family.• Many thousands of children had never even seen, let alone owned a pair of shoes.• It's disappointing that Butman doesn't ask these questions, let alone provide answers.• Keeper Judge never touched him let alone trip him.• But these images were not arbitrary, let alone trivial. 