Does one leave a terrible bruise? (6)

I believe the answer is:

abuser

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But I can't explain it at all! Could you help me understand?

(Other definitions for abuser that I've seen before include "One who reviles or a misuser of drugs" , "Bully" , "He takes undue advantage" , "One mistreating another" , "Person who over-indulges in, say, drugs or drink" .)

I've seen this clue in The Guardian.

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