Aboard is a preposition or an adverb.
Aboard means 'on or onto a ship, aircraft, train or bus'. It is the synonym of ' on board'.
- [as preposition] We finally went aboard the ship.
- [as adverb] The plane crashed into a mountainside, killing all 250 passengers aboard.
Aboard can also mean 'in or into an organization, group or company'.
- She came aboard as a chief engineer.
PhrasesAll aboard! is used to tell passengers that they should get on their ship, bus or train because it is about to leave.
Welcome aboard! is used to welcome passengers or a new employee.