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4.
A V8 engine design produced by the Ford Motor Company.
It was introduced in 1932, and was used in automobiles until the 1954 model year. In the thirties, gangsters such as Bonnie Parker and Clyde Barrow favored Fords powered by Flatheads, since they tended to be quicker than most cars of the time, they made great getaway vehicles.

It has also known that John Dillinger even wrote Henry Ford, praising his powerful Flathead V8, and thanked him for a designing quick getaway car.

The engine was also popular among moonshiners well into the 40s and early fifties.

The engine was also popular with hotrodders of the era, as well as today's hotrodders.
My 1940 Ford Coupe is powered by a Flathead V8.
by angry chocolate. September 08, 2010
 
1.
A term used to describe a person who lives "on the edge" and is very wild. The term came from Michael Flatley, who invented the Riverdance Irish Dance ensemble. "Flathead" was used to describe his fans who were very wild and crazy and the term grew from there...
Bill: This flathead I went out with last night was just too wild for my taste...
by Solar and Lunar May 13, 2007
 
2.
a derogatory term for a German American from southern Indiana, particularly from the town of Jasper, Indiana.
I wonder how much beer those flat heads in Jasper will drink this year at their Strassenfest?
by Kraut Stain March 02, 2010
 
3.
A term used to describe someone with few or no brains or common sense, resulting from repeated beating of one's head against the wall. An antiquated term from mid-20th century.
Little Joey runs out into the street.. in front of a careening ice-cream truck. Dad yells, "Joey! You flathead! Get out of the street!!"
by BlackKat65 June 21, 2010
 
5.
A white male who wears a flat-rimmed hat and is exceedingly stupid. Typically travel in posses and hang out with bumblebitches. You know a flathead is not going anywhere in life.
Why can't the library leave the Calculus books outside when they lock it up?

Because someone would steal them.

What would a flathead do with Calc book?
by TheMaskedRecommender March 29, 2013
 
6.
Slang for a mentally retarded person. Just like the word "retard" it can be used to call someone stupid that may not be mentally retarded.
Dude, sorry I messed up. I am such a flat head.
by Brettus March 26, 2008
 
7.
when the back of your head becomes fat after a night of head banging against the headboard of a bed or wall.
i woke up this morning with the worst flathead dave drove me hard last night
by a-wall9 October 16, 2009