The term "Jeep" originated in the comic strip Popeye. There it referred to an extra-dimensional cat-like critter which could travel anywhere it wanted and always said "Jeep!"
The term was applied to various military vehicles, usually large carry-all vehicles, well before it was applied to the small utility vehicles to which the name now sticks like glue.
It is the considered opinion of many that the go-anywhere nature of Popeye's Jeep "pet" is the reason why the name stuck to the 4-wheel drive small wheelbase vehicle so well.