- on board; on, in, or into a ship, train, airplane, bus, etc.: to step aboard.
- alongside; to the side.
- Baseball. on base: a homer with two aboard.
- into a group as a new member: The office manager welcomed him aboard.
- on board of; on, in, or into: to come aboard a ship.
- all aboard! (as a warning to passengers entering or planning to enter a train, bus, boat, etc., just before starting) Everyone get on!
adverb, adjective, preposition (postpositive)
- on, in, onto, or into (a ship, train, aircraft, etc)
- nautical alongside (a vessel)
- all aboard! a warning to passengers to board a vehicle, ship, etc
late 14c., probably in most cases from Old French à bord, from à “on” + bord “board,” from Frankish *bord or a similar Germanic source (see board (n.2)); the “boarding” or sides of a vessel extended to the ship itself. The usual Middle English expression was within shippes borde. The call all aboard! as a warning to passengers is attested from 1838.