The word is gluteus maximus.
Okay, no that wasn't it, but I thought it might be because in another post someone said, "He would be out on his" - and then it said, Ooo, I tried to get around the filter with a nasty word."
What could it be but another word for donkey? It's not bottom spelled the British way is it?
Edited again: No, that's not it! Quick, what are synonyms for rear end?