backside

Noun

• 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?
    

• the side of an object that is opposite its front
  • his room was toward the rear of the hotel
    

Related words

• Synonyms: 
  buttocks , rear , back end
• Antonyms: 
  front , front end , forepart