butt cheek

Bum cheeks is the very British, and fairly plain-spoken, way to refer to the buttocks — specifically the two rounded halves of them. It's informal without being particularly rude, the kind of phrase a British parent might use with a toddler or that turns up in light comedy sketches. Less crude than some alternatives, more direct than 'posterior' — bum cheeks sits comfortably in everyday casual British English as an anatomically accurate but not overly clinical description.

North American vulgar slang for a buttock, one of the two rounded halves of the rear end. Used in both literal contexts, such as anatomy or clothing discussion, and figurative ones like insults or humor. Far less clinical than gluteus but more direct than butt cheek. Among the most common vulgar anatomical terms for this body part in North American informal and casual speech.

British and Australian vulgar slang for the two rounded masses of flesh that make up the buttocks. The term is anatomically direct and carries a register somewhere between crude and clinical — less aggressive than some alternatives, but firmly informal. Used both literally in body-related contexts and figuratively in expressions of disbelief or exasperation. Also appears in comedy contexts where the exaggerated formality of 'cheeks' against the bluntness of 'arse' is part of the joke.

British and Commonwealth vulgar slang for the buttocks, specifically both halves of the rear end. Functionally equivalent to the North American ass cheeks. Used in both literal contexts and as a mildly vulgar intensifier. Common and unremarkable in casual British speech; the vulgarity registers as mild by British standards and causes little offense in informal settings. The compound is perfectly transparent in meaning and causes no ambiguity; its mildly vulgar character is simply part of the natural range of British casual speech.