1. Used to introduce something that is even more unlikely, impossible, or undesirable than what was just mentioned; to express that if something is not true, then something else is certainly not true
He can't afford a car, let alone a house.
Ele não pode pagar um carro, menos ainda que uma casa.
2. Used to emphasize a stronger or more extreme case in a comparison or negation
She won't speak to him now, and less still that she would forgive him.
Ela não fala com ele agora, menos ainda que ela o perdoaria.