on or onto a ship, plane, bus or train synonym on board We went aboard. He was already aboard the plane. The plane crashed, killing all 157 passengers aboard. All aboard! (= the bus, boat, etc. is leaving soon) Welcome aboard! (= used to welcome passengers or a person joining a new organization, etc.) See related entries: Plane travel, Train and bus travel, Parts of boats and ships, Travelling by boat or ship Word Origin late Middle English: from a- ‘to, towards’ (expressing motion) + board, reinforced by Old French à bord.