look ‧ out /ˈlʊk-aʊt/ BrE AmE noun
1 . be on the lookout for somebody/something to continuously watch a place or pay attention in order to find something you want or to be ready for problems or opportunities ⇨ look out for :
We’re always on the lookout for new business opportunities.
Police were on the lookout for anyone behaving suspiciously.
2 . keep a lookout to keep watching carefully for something or someone, especially for danger
keep a lookout for
We were instructed to keep a lookout for enemy aircraft.
When you’re driving, keep a sharp lookout (=watch extra carefully) for cyclists.
3 . PERSON [countable] someone whose duty is to watch carefully for something, especially for danger
4 . PLACE [countable] a place for a lookout to watch from
5 . that's/it's somebody's lookout British English informal used to say that someone is responsible for deciding what they will do, and will have to suffer any bad results:
If he wants to keep seeing her, that's his lookout.