patrol

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act of moving about an area especially by an authorized and trained person or group, for purposes of observation, inspection, or security.
• noun A person or group of persons who perform such an act.
• noun A military unit sent out on a reconnaissance or combat mission.
• noun One or more military vehicles, boats, ships, or aircraft assigned to guard or reconnoiter a given area.
• noun A division of a Boy Scout troop or Girl Scout troop consisting of between six and eight children.
• intransitive verb To engage in a patrol of.
• intransitive verb To engage in a patrol.

from The Century Dictionary.

• To go the rounds in a camp or garrison; march about in order to check disorder or irregularities, as a guard.
• To go the rounds in a city, as a body of police.
• To perambulate or traverse in all directions, as a patrol in a camp, garrison, town, harbor, etc., for the purpose of watching, guarding, or protecting; go over or through in all directions as a patrolman.
• noun A walking or marching round, as in a camp, garrison, town, or other place, in order to watch and protect it.
• noun The guard or persons who thus go the rounds; specifically, a police constable whose duty it is to perambulate a “beat” or district for a certain number of hours, for the protection of life and property, and the preservation of the peace; also, such constables collectively.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To go the rounds along a chain of sentinels; to traverse a police district or beat.
• transitive verb To go the rounds of, as a sentry, guard, or policeman
• noun A going of the rounds along the chain of sentinels and between the posts, by a guard, usually consisting of three or four men, to insure greater security from attacks on the outposts.
• noun A movement, by a small body of troops beyond the line of outposts, to explore the country and gain intelligence of the enemy's whereabouts.
• noun The guard or men who go the rounds for observation; a detachment whose duty it is to patrol.
• noun Any perambulation of a particular line or district to guard it; also, the men thus guarding
• noun See Boy Scout.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To go the rounds along a chain of sentinels; to traverse a police district or beat.
• verb transitive To go the rounds of, as a sentry, guard, or policeman; as, to patrol a frontier; to patrol a beat.
• noun military A going of the rounds along the chain of sentinels and between the posts, by a guard, usually consisting of three or four men, to insure greater security from attacks on the outposts.
• noun military A movement, by a small body of troops beyond the line of outposts, to explore the country and gain intelligence of the enemy's whereabouts.
• noun military The guard or men who go the rounds for observation; a detachment whose duty it is to patrol.
• noun Any perambulation of a particular line or district to guard it; also, the men thus guarding; as, a customs patrol; a fire patrol.
• noun Scouting A unit of a troop, typically composed of around eight boys.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb maintain the security of by carrying out a patrol
• noun a detachment used for security or reconnaissance
• noun a group that goes through a region at regular intervals for the purpose of security
• noun the activity of going around or through an area at regular intervals for security purposes