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keep (one's) temper
To refrain from becoming angered, enraged, or upset due to some provocation; to maintain control of one's composure despite being angry or upset. You're a good driver, but if you don't do a better job of keeping your temper when other drivers make mistakes, you're going to end up causing a crash some day. It's hard to keep my temper with the kids after being kept awake by them all night long.
keep one's temperand hold one's temper
to hold back an expression of anger. (The opposite of lose one's temper.) She should have learned to keep her temper when she was a child. Sally got thrown off the team because she couldn't hold her temper.