1. Verb - to press up against or to jostle.
2. Noun - the end part of a rifle or shotgun or machinegun that rests against the shoulder or pectoral muscles to increase stability during firing.
3. Noun - the part of a human being that knows wind and earth. The buttocks and anus of a person.
4. Noun - the recipient or target of a joke.
Ever since Father O'Malley was caught butting that butt into that young choirboy's butt, he has become the butt of many cruel jokes.