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
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 Gerard Irick October 19, 2010
by knuckleheadwittness January 26, 2012
An honors physics student of ability but who lacks the conventional expression of said ability (i.e. homework completion, class appropriateness). May or may not get high grades.
by Pelota January 29, 2010