Aboard is defined as being on or inside a vehicle, ship or airplane.
(adverb)An example of coming aboard would be passengers who come into the train car.
See aboard in Webster's New World College Dictionary
adverb
Origin: ME abord < OFr a bord: see board
See aboard in American Heritage Dictionary 4
adverb
Origin:
Origin: Middle English abord
Origin: : a-, on; see a-2
Origin: + bord, ship (from Old English bord)
.Learn more about aboard