plaster of paris
What does plaster of paris mean?
The arse, reached by a two-step rhyming chain. 'Arse' rhymes with 'bottle and glass' (clipped to 'bottle'), 'bottle' becomes 'Aristotle' (clipped to 'Aris'), and 'Aris' rhymes with 'plaster of Paris'. By the time you say it, nobody outside the East End knows what you mean — which was always the point.
Origin
A famous double-rhyme: arse → bottle and glass → bottle → Aristotle → Aris → plaster of Paris. One of the showiest examples of how deep Cockney rhyming slang stacks.