1. call it a day to quit work and go home; to say that a day’s work has been completed.
I’m tired. Let’s call it a day.
2. clear the air to get rid of doubts or hard feelings. (Also literal. Sometimes this is said about an argument or other unpleasantness.)
All right, let’s discuss this frankly. It’ll be better if we clear the air.
3. cock-and-bull story a silly, made-up story; a story that is a lie.
Don’t give me that cock-and-bull story.
4. come (a)round 1. finally to agree or consent (to something).
I thought he’d never agree, but in the end he came around.
5. come down hard on someone or something to attack vigorously; to scold someone severely.
Tom’s parents really came down hard on him for coming home late.
6. fall back on someone or something to turn to someone or something for help. (Also literal.)
Bill fell back on his brother for help.
7. give a good account of oneself to do (something) well or thoroughly.
John gave a good account of himself when he gave his speech last night.
8. play cat and mouse (with someone) to alternate between kinds of behavior when dealing with someone, often in matters of pursuit.
The police played cat and mouse with the suspect until they had sufficient evidence to make an arrest.
9. serve as a guinea pig [for someone] to be experimented on; to allow some sort of test to be performed on someone. (A guinea pig was once the quintessential experimental animal.)
10. when the chips are down at the final, critical moment; when things really get difficult.
When the chips are down, I know that I can depend on Jean to help out.