From blunder + -head.
blunderhead (plural blunderheads)
- Someone who habitually makes mistakes or blunders
1871, Oliver Optic, Desk and Debit[1]:"What do you suppose I cared whether I waked you or not, you blunderhead.
1851, Goold Brown, The Grammar of English Grammars[2]:At the rate of this thick-skulled blunderhead, every plow-jobber shall take upon him to read upon divinity."