An expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements or in its grammatically atypical use of words.
Idiom:
let alone (something)
Meaning:
to not mention something, to say nothing of something
Example:
I do not have enough money to go to a movie let alone go on a holiday.
List of common idioms, their meanings and examples of their usage in sentences
Idioms can be a powerful linguistic tool only when they are used in the right way in the right places.