What does aboard mean?
The definition of aboard
A*board”, adv.
Etym: [Pref. a- on, in + board.]

On board; into or within a ship or boat; hence, into or within a railway car.
2 Alongside; as, close aboard. Naut.: To fall aboard of, to strike a ship’s side; to fall foul of.

— To haul the tacks aboard, to set the courses.
— To keep the land aboard, to hug the shore.
— To lay (a ship) aboard, to place one’s own ship close alongside of (a ship) for fighting.

A*board”, prep.
1 On board of; as, to go aboard a ship.
2 Across; athwart. [Obs.] Nor iron bands aboard The Pontic Sea by their huge navy cast. Spenser.