On board; into or within a ship or boat; hence, into or within a railway car.
We all climbed aboard.
On or onto a horse, a camel, etc.
To sling a saddle aboard.
On base.
He doubled with two men aboard, scoring them both.
Into a team, group, or company.
The office manager welcomed him aboard.
Alongside.
The captain laid his ship aboard the enemy's ship.
On board of; onto or into a ship, boat, train, plane.
We all went aboard the ship.
Onto a horse.
Across; athwart; alongside.