It was named after a WWII fighter plane, not a wild horse: It is generally believed that the Mustang acquired its name from the wild unbroken North American horse known as a Mustang. In truth, the car was named for the famous air war-winning North American P-51 Mustang, the WWII mount of famed test pilot and ace Chuck Yeager.
And what was the plane named after? A delicate flower found in mountain meadows? :rolleyes