adverb / preposition
aboard
uh-BORD/əˈbɔːrd/
On or into a vehicle carrying people.
Passengers step aboard the train while others sit inside.

Etymology
Probably from a phrase meaning “on the ship’s side,” aboard reflects the extension of a vessel’s sides to the whole vessel. Being on a vessel then supplies the image for joining a group or shared effort.
In context
If you're short on time, climb aboard the ferry,
Edmond Dantes is a fine young sailor, nineteen years old, aboard the Pharaon.