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
Origin: ME abord < OFr a bord: see board
See aboard in American Heritage Dictionary 4
Origin: Middle English abord
Origin: : a-, on; see a-2
Origin: + bord, ship (from Old English bord).
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