We were sinking fast, and the captain gave the order to abandon ship.

abandon 是动词，意思是"放弃、抛弃、遗弃"，通常指在紧急情况下被迫离开或放弃某物或某地。在这个句子中，abandon ship 是一个固定短语，意思是"弃船"，指船员在船只即将沉没或发生严重事故时离开船只。