An idiom for working as something

1. What is idiomatic expression of doing something?

What is idiomatic expression of doing something?

Idiomatic expressions are groups of words with an established meaning unrelated to the meanings of the individual words. Sometimes called an expression, an idiom can be very colorful and make a 'picture' in our minds. Some common idiomatic expressions: He let the cat out of the bag (accidentally told a secret).