backside

英[bæk'saɪd;'bæksaɪd] 美['bæksaɪd]

1. the side of an object that is opposite its front;

"his room was toward the rear of the hotel"

2. the fleshy part of the human body that you sit on;

"he deserves a good kick in the butt"

"are you going to sit on your fanny and do nothing?"