fathead(noun) noun1. a man who is a stupid incompetent foolSimilar word(s): bozo, cuckoo, goof, goofball, goose, jackass, zanyDefinition categories: person, fool, muggins, sap, saphead, tomfoolSentences with fathead as a noun:- Donny, you fathead! You forgot to put the milk in the fridge and now it's spoiled!