ad.

1. 在船（或飛機，車）上；上船（或飛機，車）
   All passengers aboard fell into the river.

   船上所有乘客皆落入河中。

2. 並排在邊上

prep.

1. 在（船，飛機，車）上；進入，上（船，飛機，車）
   They were the last two to go aboard the ship.

   他們是最後兩位上船的。

adv.

prep.

1. on or into (a ship, train, or other vehicle).
2. Baseball  on base.