From the 1930's (circa). Refers to a person of questionable intelligence. The size of the brain being given relative size of a human knuckle. Similar to pinhead.
by The Phat Doctor December 27, 2004
by Merrily McCarthy July 17, 2003
Someone of limited intelligence and with a mean nature. Who prefers using their knuckles/fists, to using their head.
by IanM September 14, 2003
Someone who has just made a mistake or done something wrong. Often used in a joking manner between friends.
After arriving at the ski resort Pat discovered that he had forgot his skis to which his friends responded "Pat, you're a knuckle head!".
by zantern June 22, 2005
by J-Wilk May 06, 2007
Engine produced by the Harley Davidson Motorcycle Company from(1936 to 1947). The engine consists of an overhead-valve v-twin design with covers on the valves that resembled knuckles, hence the name of "knucklehead".
by The B-rad October 13, 2006
by Tank238 October 14, 2012