ETYM French patrouille, Old Fren. patouille. Related to Patrol.
1. A detachment used for security or reconnaissance.
2. A group that goes through a region at regular intervals for the purpose of security.
3. The activity of going around or through an area at regular intervals for security purposes; SYN. patrolling.

To maintain the security of by carrying out a control; SYN. police.
To carry out a patrol