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 28, 2004
by Merrily McCarthy July 18, 2003
by J-Wilk May 07, 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 14, 2006
by Tank238 October 15, 2012
Don't be a knucklehead you understand what's being said.
by Gerard Irick October 19, 2010
by knuckleheadwittness January 27, 2012