Copper's round, or is a square? (4)

I believe the answer is:

beat

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'copper's round' is the definition.
'beat' can be an answer for 'round' (synonyms). I am not certain of the 'copper's' bit.

'is a square?' is the wordplay.
'is' becomes 'be'.
'square?' becomes 't' (a T-Square is a technical drawing instrument).
'be'+'a'+'t'='BEAT'

'or' is the link.

Can you help me to learn more?

(Other definitions for beat that I've seen before include "Surpass (a score)" , "tired" , "Strike; stir vigorously" , "Defeat, strike" , "Strike (a drum)" .)

I've seen this clue in The Guardian.

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