To have a sexual relationship with someone, or a British slang term for casual intimacy.
British military slang, origin uncertain, possibly imitative or from earlier dialectal words. Gained popular usage in mid-20th century British English, possibly from acronym BOFF (Base Operations Forward Force).
Military slang from WWII often involved creating quick, punchy words for things soldiers didn't want to say formally—and this one stuck around in British English long after the war ended.
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