'copper' (slang 'police officer') originates from mid 19th-century English, possibly derived from the verb 'to cop' meaning 'to seize' or from the copper badges or buttons worn by police officers.

'copper' (the metal name) changed from Middle English 'coper' (or 'copper'), borrowed from Old English 'coper', which in turn came from Latin 'cuprum' via Old French forms; the Latin 'cuprum' traces back to Greek 'Kyprios' meaning 'of Cyprus' (because much copper came from Cyprus).

Initially it referred specifically to the metal sourced from Cyprus; over time it became the general name for the element copper and later gained figurative and slang senses, including 'police officer'.