1832, abbreviation of
omnibus (q.v.). The Eng. word is simply a Latin dative plural ending. The verb meaning "transport students to integrate schools" is first recorded 1961. Verb meaning "clear tables in a restaurant" is first attested 1913, probably from the four-wheeled cart used to carry dishes. To
miss the bus, in the fig. sense, is from 1915.
Busman's holiday "leisure time spent doing what one does for a living" (1893) is probably a reference to London bus drivers riding the buses on their days off.