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have at someone
to go at someone; to attack someone. The boys had at the gang members and gave them a beating. I just knew John was going to have at Fred.
Attack; also, make an attempt at. For example, Urging the dog on, he said, " Go on, Rover, have at him," or It's time to have at straightening out these files. [Late 1300s]
To engage something in a vigorous, enthusiastic, or aggressive way: Here's the work you need to do, so have at it! The dog really had at the bones that were left in the garbage. The teacher took me aside and had at me for my bad behavior.