let alone Not to mention; much less:
更不用提；更别说：“Their ancestors had been dirt poor and never saw royalty,let alone hung around with them”(Garrison Keillor)
“他们的祖先穷得要命,从来没有见过王族成员,更不用说和他们在一起了”(加里森·谢勒)
There isn't enought room for us,let alone six dogs and a cat
I haven't decided on the menu yet,let alone bought the food.
I haven't decided where to go,let alone when to leave.