Buttock (noun)

Either of two rounded fleshy protuberances that form the lower part of the human trunk and are located on either side of the anus.

Origin:

From middle english buttek, from old english buttuc, meaning 'a bulge or swelling'.

Examples:

1. She rubbed her sore buttock after sitting for too long on a hard chair.
2. The horse's flanks were slick with sweat, and its buttock muscles rippled.
3. His tight pants accentuated the shape of his buttocks.
4. She couldn't reach her lower back, so she asked him to massage her buttocks.
5. The dancers gyrated their hips, causing their buttocks to jiggle.