ad.

1. 在船（或飞机，车）上；上船（或飞机，车）
   All passengers aboard fell into the river.

   船上所有乘客皆落入河中。

2. 并排在边上

prep.

1. 在（船，飞机，车）上；进入，上（船，飞机，车）
   They were the last two to go aboard the ship.

   他们是最后两位上船的。

adv.

prep.

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