Origin of the name

There are many explanations of the origin of the word jeep, all of which have proven difficult to verify. The most widely held theory is that the military designation of GP begat the term Jeep and holds that the vehicle bore the designation GP (for Government Purposes or General Purpose), which was phonetically slurred into the word jeep. However, an alternate view launched by R. Lee Ermey, on his television series Mail Call, disputes this, saying that the vehicle was designed for specific duties, and was never referred to as "General Purpose" and it is highly unlikely that the average jeep-driving GI would have been familiar with this designation. The Ford GPW abbreviation actually meant (G for government use, P to designate its 80-inch (2,000 mm) wheelbase and W to indicate its Willys-Overland designed engine).

Many, including Ermey, suggest that soldiers at the time were so impressed with the new vehicles that they informally named it after Eugene the Jeep, a character in the Popeye cartoons created by E. C. Segar. Eugene the Jeep was Popeye's "jungle pet" and was "small, able to move between dimensions and could solve seemingly impossible problems."

Words of the Fighting Forces by Clinton A. Sanders, a dictionary of military slang, published in 1942, in the library at The Pentagon gives this definition:

Jeep: A four-wheel drive vehicle of one-half- to one-and-one-half-ton capacity for reconnaissance or other army duty. A term applied to the bantam-cars, and occasionally to other motor vehicles (U.S.A.) in the Air Corps, the Link Trainer; in the armored forces, the ½-ton command vehicle. Also referred to as "any small plane, helicopter, or gadget."

This definition is supported by the use of the term "jeep carrier" to refer to the Navy's small escort carriers.

Early in 1941, Willys-Overland demonstrated the vehicle's off-road capability by having it drive up the steps of the United States Capitol, driven by Willys test driver Irving "Red" Haussman, who had recently heard soldiers at Fort Holabird calling it a "jeep." When asked by syndicated columnist Katherine Hillyer for the Washington Daily News (or by a bystander, according to another account) what it was called, Irving answered, "It's a jeep."

Although the term was also military slang for vehicles that were untried or untested, this exposure caused all other jeep references to fade, leaving the 4x4 with the name.