Hip is the side of your butt Butt is the person's ass/bottom/posterior, They're all used interchangeably. Buttock is derived from the word butt Butt is mostly used by teenagers/children's to avoid a more extreme offensive language (it's slightly less disrespectful than ass but I'd be cautious to use this word) Ass is more commonly used with adults Posterior means back end of something OR butt Bottom is the lower part of something OR butt (It's the most respectful term out of all)