Definition of "on board"

on board

adjective
not comparable
1. On or in a means of transportation.
  Quotations
  There is an hour or two, after the passengers have embarked, which is disquieting and fussy. Mail bags, so I understand, are being put on board. Stewards, carrying cabin trunks, swarm in the corridors. Passengers wander restlessly about or hurry, with futile energy, from place to place.
  1915, G[eorge] A. Birmingham [pseudonym; James Owen Hannay], chapter I, in Gossamer, New York, N.Y.: George H. Doran Company
2. (idiomatic) Joining in or participating.
3. (idiomatic) Agreeing or supporting.
  Quotations
  The ships' successes made Hitler quite the fan of them, and he supported the idea of more being converted and sent out soon. And so, with the Führer on board, albeit not literally, another six vessels were rapidly placed under conversion.
  2021 February 17, Drachinifel, 20:52 from the start, in German Merchant Raiders of WW2 - Gentleman Raiders of the High Seas‎, archived from the original on 4 December 2022
4. (idiomatic) Into itself or oneself.
  Quotations
  Soccer players certainly tend not to take fluids on board.
  1991, David R. Lamb, Melvin H. Williams, Ergogenics: Enhancement of Performance in Exercise and Sport
interjection
1. The stereotypical cry of pirates when boarding a ship for close quarters combat.