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MostAn idiom is an expression whose meaning cannot be directly derived from the meanings of the words it contains. Hence one of the meanings of the word “idiomatic” is “containing/being an idiom”, as in:
“Pulling someone’s leg” is an idiomatic expression.
However, this is not the most common meaning of the word “idiomatic”. When English speakers speak about something being idiomatic, it means that it sounds natural. For example, trying to explain a difference between “wait for me” and “wait at me”, a native speaker could say:
“Wait for me!” is idiomatic, while “Wait at me!” is not.
In this context, the intended meaning is not that “wait for me” is an idiom (on the contrary, it is quite clear what it means). “Idiomatic” simply means “how a native speaker would say it”, and this is the most common sense in which this adjective is used.
