1
be on the lookout (for sth)
表示保持警惕，留意某事。
The police are on the lookout for any suspicious activity.
警方正在留意任何可疑活动。
瞭望者；警戒员
先理解核心含义，再看它在真实句子里的用法。
瞭望者；警戒员
A person who watches for danger, an enemy, or a hoped-for event.
The police are on the lookout for any suspicious activity.
警方正在留意任何可疑活动。
能看到周围区域的有利位置。
A vantage point with a view of the surrounding area.
瞭望员
a person employed to keep watch for some anticipated event
一段监视来犯敌人、警察等的时间。
A session of watching for an approaching enemy, police, etc.
瞭望台
an elevated post affording a wide view
The lookout spotted the approaching ship long before it reached the harbor.
瞭望员在船只抵达港口之前很久就发现了它。
From the lookout, we could see the entire valley spread out below us.
从瞭望台上，我们可以看到整个山谷在我们下方展开。
The park built a new lookout at the top of the hill for visitors to enjoy the view.
公园在小山顶上建了一个新的观景台，供游客欣赏风景。
表示保持警惕，留意某事。
The police are on the lookout for any suspicious activity.
警方正在留意任何可疑活动。
与“be on the lookout”类似，但更强调主动监视。
Keep a lookout for the postman; I'm expecting a package.
留意邮递员，我在等一个包裹。
指担任瞭望员或警戒者。
He acted as a lookout while the others entered the building.
他负责放哨，其他人进入大楼。
Not this
You should lookout for the warning signs.
Use this
You should look out for the warning signs.
lookout 是名词，意为“瞭望员”或“注意（名词）”，不能用作动词短语。应使用动词短语 look out for 来表示“注意、提防”。
Not this
He works as a look out at the construction site.
Use this
He works as a lookout at the construction site.
lookout 是单一名词，不应分写为两个词。分写会变成动词短语，不符合名词用法。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
留意；警戒
The police are on the lookout for a suspicious man.
警方正在留意一名可疑男子。
保持警戒；注意
Please keep a lookout for any vehicles coming down the road.
请留意路上驶来的车辆。
担任瞭望员；放哨
He acted as a lookout while his friends broke in.
他朋友闯进去时，他在外面放哨。
瞭望塔
The fire lookout tower gives a wide view of the forest.
这座防火瞭望塔可以一览森林全景。
观景台
The cliff lookout point is popular with hikers.
这个悬崖观景台很受徒步者欢迎。
留心；密切注意
The police are on the lookout for a white van seen near the scene.
警方正在密切注意案发现场附近出现过的一辆白色面包车。
保持警戒；监视
You stay here and keep a lookout while I check the back door.
你待在这里保持警戒，我去检查后门。
那是你自己的事；你自己负责
If you don't study for the exam, that's your lookout.
如果你不复习考试，那是你自己的事。
发短 /ʊ/ 音 (如 good, book)
Use lookout naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
联想短语 look out「小心/向外看」——瞭望员或瞭望台就是负责 lookout 向外观察、警惕危险的人或位置。
语域：neutral 常见场景：日常对话、旅游观景、警戒/监视场景 该词语气中性，日常口语和书面语中都常用。多用于指瞭望员、瞭望台/观景处或警戒/监视的动作，具体含义常依搭配而定，如‘keep a lookout’表示‘留意守望’。通常无明显的正式或随意之分。
常用于短语 on the lookout (for)
Dictionary facts from ECDICT, WIKTIONARY.