1900, "A word used in the early days of motor vehicles for a horse-drawn vehicle" [OED], from French, from hippo- "horse" + ending from automobile.
Entries linking to hippomobile
hippo-
before vowels, hipp-, word-forming element meaning "horse," from Greek hippo-, from hippos "horse," from PIE root *ekwo- "horse."
automobile adj.
"self-moving, self-movable," 1883, in reference to electric traction cars, from French automobile (adj.), 1861, a hybrid from Greek autos "self" (see auto-) + French mobile "moving," from Latin mobilis "movable" (see mobile (adj.)).