but·tock 
/ˈbʌtək/ noun
plural but·tocks /ˈbʌtək/ noun [count] : either of the two soft parts of the body that a person sits on
▪ the baby's left/right buttock — usually plural ▪ The shirt is long enough to cover your buttocks. — see picture at human
▪ the baby's left/right buttock — usually plural ▪ The shirt is long enough to cover your buttocks. — see picture at human
