Definitions

1. noun

a bruise or swelling on the buttocks, especially one caused by sitting on a heavy object.

“After falling onto the stack of boxes, he had a large sackbutt that was sore to the touch.”

2. verb

to bruise or give a sore on the buttocks, especially by sitting on a heavy object.

“The heavy toolbox had left him with a badly sackbutted buttock.”