Onboard/ˈɑːnbɔːrd/ Definition 1 of 3Pro Tip 1/3Joining Action Often suggests you're joining others already present or moving into a vehicle. Let's go onboard and join the crew. Pro Tip 2/3Not for Facilities Don't use 'onboard' to describe objects inside a vehicle, only for people or animals. The luggage is on the ship, not onboard. Pro Tip 3/3Transition Phase Implies the moment of transition from not being on a vehicle to being inside it. She stepped onboard just before the doors closed.