From Longman Dictionary of Contemporary Englishkeep a lookoutkeep a lookoutWATCHto keep watching carefully for something or someone, especially for dangerkeep 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. → lookout
Examples from the Corpus
keep a lookout• Then, with a watchful eye, it can keep a lookout for potential prey without revealing its presence.• Soldiers kept a lookout for enemy planes through the night.• And send a couple of your boys up here to keep a lookout.• From his present position, Larsen would be better placed to keep a lookout for trouble and provide backup. 