Is it ensure, insure, or assure?
1610s, "a medium through which a drug or medicine is administered," also "any means of conveying or transmitting," from French véhicule, from Latin vehiculum "means of transport, a vehicle," from vehere "to carry," from PIE *wegh- "to go, transport in a vehicle" (cf. Old English wegan "to carry;" Old Norse vegr, Old High German weg "way;" Middle Dutch wagen "wagon;" see wagon). Sense of "cart or other conveyance" first recorded 1650s.
vehicle ve·hi·cle (vē'ĭ-kəl)
A substance of no therapeutic value that is used to convey an active medicine for administration.