on first or second or third base; "Their second homer with Bob Allison aboard" on a ship, train, plane or other vehicle part of a group; "Bill's been aboard for three years now" side by side; "anchored close aboard another ship
If you are aboard a ship or plane, you are on it or in it. She invited 750 people aboard the luxury yacht, the Savarona They said goodbye to him as he got aboard the train at Union Station. = on board Aboard is also an adverb. It had taken two hours to load all the people aboard = on board