at sea

1. 在大海上
   He spent 3 months at sea.

   他在海上航行了三個月。

2. 茫然
   I'm rather at sea. Could you explain that again?

   我實在不太明白，你能再解釋一下嗎？

beyond the sea(s)

1. 在海外
   For many years he had lived beyond the seas.

   他曾在海外住了多年。

by sea

1. 由海路
   He sent his heavy boxes by sea.

   他將那沉重的箱子海運。

go to sea

1. 當水手
   When he was a boy, his greatest wish was to go to sea.

   他小時候最大的願望就是去當水手。

half seas over

1. 酒醉
   Within an hour he was half seas over and incapable of getting home by himself.

   不到一個小時他就醉了，沒法獨自回家。

on the sea

1. 在海邊
   The city is on the sea.

   這個城市位於海邊。

put to sea

1. 出航
   The ship was unable to put to sea on account of the gale.

   由於大風船未能出航。

• at sea
  
  1. sailing on the sea.
  2. (also all at sea) confused; uncertain.
• put (out) to sea
  leave land on a voyage.
• one's sea legs
  one's ability to keep one's balance and not feel seasick on board a moving ship.