Past tense of shop: to visit stores to look at or buy goods, or to inform on someone to authorities.
From Middle English 'shoppe' (a booth or stall), which came from Old English origins. The 'inform on' meaning emerged in British slang in the 1930s.
The dual meaning of 'shopped'—buying things versus betraying someone—shows how British slang repurposed a everyday word into something darkly humorous, especially during wartime when informing on neighbors was a real danger.
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