noun A vantage point with a view of the surrounding area.
noun A session of watching for an approaching enemy, police, etc.
We kept a lookout all night, but nobody came.
noun A person on watch for approaching enemy, police, danger, etc.
The raid failed when the lookout noticed the enemy group.
noun A subject for observation; a prospect or view.
noun One's perspective, outlook; hence, one's responsibility. (used with a possessive pronoun or a noun in a possessive form).
Every person's interest is his own lookout.
noun An observation window.
noun A joist that extends in cantilever out from the exterior wall (or wall plate) of a building, supporting the roof sheathing and providing a nailing surface for the fascia boards.