keep a lookout 保持警惕
watchman 守门人
sentry 哨兵
lookout tower 瞭望塔
1. The lookout man signaled that the coast was clear.
警戒人员发出信号，表示安全了。
2. They need a lookout man to watch the entrance.
他们需要一名警戒人员来盯着入口。
A: Has the lookout man spotted anything unusual?
A：警戒人员发现什么异常了吗？
B: No, everything seems calm so far.
B：没有，目前一切看起来都很平静。
1) 警戒人员
2) 哨兵
3) 监视者
1. 警戒人员
e.g.
The lookout man is stationed at the gate.
警戒人员驻守在门口。
noun phrase
1. A person whose role is to watch for danger or approaching enemies.
Synonym: lookout, sentry, watchman