Longman Dictionary of Contemporary English - patrol

~1 v patrolled, patrolling I always+adv/prep, 1 to go around the different parts of an area or building at regular times to check that there is no trouble or danger  (waters patrolled by enemy submarines | Armed guards with dogs patrolled the exhibition.) 2 to drive or walk repeatedly around an area in a threatening way  (Gangs of youths patrolled the streets at night.) ~2 n 1 the act of going around different parts of an area at regular times to check that there is no trouble or danger  (Security guards carry out regular patrols of the factory premises. | patrol duty | on patrol)  (submarines on patrol in the North Atlantic | patrol boat/car (=used by the army or police)) 2 a group of police, soldiers, vehicles, planes etc sent out to search a particular area  (the US border patrol) 3 a small group of boy scouts or girl guides  (- see also highway patrol)