Tennis Buttock

Synonyms
The anatomical Latin name for the buttocks is nates (/ˈneɪtiːz/ or NEY-teez in English), which is plural; the singular, natis (buttock), is rarely used. As buttocks are an object of both shame and fascination, it is not surprising that there are many colloquial terms, euphemistic, ironic or other, to refer to them. These include the following:
• backside, posterior, behind and its derivates (hind-quarters, hinder or the childish homophone heinie (US usage only), strictly the whole body behind the hind leg-trunk attachment), rear or rear-end, derrière (French for "behind") - all strictly positional descriptions, as the inaccurate use of rump (as in 'rump roast', after a 'hot' spanking), thighs, upper legs; analogous are:
• aft, stern and poop, naval in origin; in nautical jargon, buttocks also designates the aftermost portion of a hull above the water line and in front of the rudder, merging with the run below the water line