A portable toilet or lavatory, especially one used by soldiers in the field or workers on construction sites; slang for an outdoor privy.
Origin unclear, possibly from 'dun' (color) or combining 'dung' with 'kin' (kindred/related), or from rhyming slang 'Dun and Bradstreet' corrupted to 'dunnakin.' Military slang from early 20th century.
British soldiers used 'dunnakin' as a euphemism that was crude enough to be funny but not offensive—it's the kind of soldiers'-barracks humor that created some of English's most enduring slang.
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