ETYMOLOGY
from French hippomobile , from hippo- from Greek ἵππος (horse), from hippos (horse) + ‑mobile after automobile
EXAMPLE
“… Speaking generally, it is the bad driver who uses the horn most, and so brings motor-cars into disrepute by creating unnecessary alarm to other travellers. In overtaking a horse-drawn vehicle it is best to sound the horn when some distance behind, and so soon as it is seen that the signal has been noticed to avoid its use again until past the ” hippomobile.” Of course it is sometimes necessary to use the horn when quite close to a horse-drawn vehicle for instance, when it unexpectedly turns out across one’s path; but even on such occasions two moderate and short blasts are generally sufficient to warn the driver. …”
From: The Motor-Car Journal
London, Friday, March 17th, 1899
Comments, ‘The Motor-Car Horn’
Lexicophilia 