Pronunciation: (u-bôrd', u-bōrd'), [key]
1. on board; on, in, or into a ship, train, airplane, bus, etc.: to step aboard.
2. alongside; to the side.
3. Baseball.on base: a homer with two aboard.
4. all aboard!(as a warning to passengers entering or planning to enter a train, bus, boat, etc., just before starting) Everyone get on!
5. 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.