"{not} in a (million|thousand|billion) years" 的定义和意义

What is the origin of the idiom "not in a million years" and when to use it?

The phrase "not in a million years" is an idiom used to express extreme certainty that something will never happen. The origin of this phrase is not precisely documented, but it likely emerged from the idea that a million years is an incredibly long time, making the occurrence of a particular event extremely unlikely.