A vantage point with a view of the surrounding area.
A session of watching for an approaching enemy, police, etc.
We kept a lookout all night, but nobody came.
A person on watch for approaching enemy, police, danger, etc.
The raid failed when the lookout noticed the enemy group.
A subject for observation; a prospect or view.
One's perspective, outlook; hence, one's responsibility. (used with a possessive pronoun or a noun in a possessive form).
Every man's interest is his own lookout.