stand by
stand by {v.}
1. To be close beside or near.
Mary could not tell Jane the secret with her little brother standing by.
Would you just stand by and watch the big boys beat your little brother?
2. To be near, waiting to do something when needed.
The policeman in the patrol car radioed the station about the robbery, and then stood by for orders.
Lee stood by with a fire extinguisher while the trash was burning.
3. To follow or keep (one's promise).
He is a boy who always stands by his promises.
4. To be loyal to; support; help.
When three big boys attacked Bill, Ed stood by him.
Some people blamed Harry when he got into trouble, but Joe stood by him.
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Source: A Dictionary of American Idioms