Is it ensure, insure, or assure?
1829, "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, in London from 1829. In reference to legislation, the word is recorded from 1842. Meaning "man or boy who assists a waiter at a restaurant" is attested from 1888 (cf. busboy). As an adjective in English from 1842.