1809, "mobile or field hospital," from Fr.
(hôpital) ambulant, lit. "walking (hospital)," from L.
ambulans (gen.
ambulantis), from
ambulare "to walk" (see
amble). Not common until meaning transferred from "hospital" to "vehicle for conveying wounded from field" (1854) during the Crimean War.
Ambulance-chaser as a contemptuous term for a type of lawyer dates from 1897.