A person who keeps watch for danger or trouble. The pirates posted a lookout to warn them of approaching ships.
A place from which to keep watch or view the surrounding area. The hikers reached the lookout and admired the breathtaking view of the valley below.
The act of keeping watch; vigilance. The security team maintained a constant lookout for any suspicious activity.
Responsibility or concern for one's own affairs or safety. If you choose to ignore the warnings, that's your lookout.