on board (not comparable)

1. On or in a means of transportation.

   Baby on board

   Even when I am on board the plane, I can never feel secure that my luggage is, too.

   • 1915, G[eorge] A. Birmingham [pseudonym; James Owen Hannay], chapter I, in Gossamer, New York, N.Y.: George H. Doran Company, OCLC 5661828 ↗:

     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.

2. (idiomatic) Joining in or participating.

   Is that new teammate properly on board yet?

3. (idiomatic) Agreeing or supporting.

   It’s a good idea, but let’s see if we can get a few more of the management team on board.

4. (idiomatic) Into itself or oneself.
   • 1991, David R. Lamb, ‎Melvin H. Williams, Ergogenics: Enhancement of Performance in Exercise and Sport

     Soccer players certainly tend not to take fluids on board.

• off board

• French: à bord de
• German: an Bord
• Russian: на борту́
• Spanish: a bordo

1. On a vehicle or vessel; aboard.