1829, "long-bodied, four-wheeled public vehicle with seats for passengers," from French (voiture) omnibus "(carriage) for all, common (conveyance)," from Latin omnibus "for all," dative plural of omnis "all" (see omni-). Introduced by Jacques Lafitte in Paris in 1819 or '20, used in London from 1829.
As an adjective, in reference to legislation, "designed to cover many different cases, embracing numerous distinct objects," recorded from 1835; in U.S., used especially of the Compromise of 1850. Noun meaning "man or boy who assists a waiter at a restaurant" is attested from 1888 (compare busboy).