aboard (Adverb) — On a ship, train, plane or other vehicle.
aboard (Adverb) — (baseball) on first, second or third base. ex. "Their second homer with Bob Allison aboard"
aboard (Adverb) — Side by side. ex. "anchored close aboard another ship"
aboard (Adverb) — Part of a group. ex. "Bill's been aboard for three years now"
aboard (Preposition) — On board of. ex. "We all went aboard the ship"