someone whose neck is as wide or wider than his/her head so that the whole head-neck region looks like a giant thumb. A weak chin might add to this effect.
I'd never go out with him because he's a thumbhead.
by Andy Kelly April 04, 2008
People with very light blonde hair.
"Hey guys. I just bleached my hair. I'm a thumb head now. lol"
by Rachael C December 05, 2007