sə(r)ˈvālən(t)s also -lyən- noun
( -s )
Etymology: French, from surveiller to watch over (from sur- + veiller to watch, from Latin vigilare to watch, wake, from vigil awake, watchful) + -ance — more at vigil
1. : close watch kept over one or more persons : continuous observation of a person or area (as to detect developments, movements, or activities)
place a suspected person under police surveillance
surveillance of air traffic by radar
2. : close and continuous observation for the purpose of direction, supervision, or control
club facilities … are conducted under close surveillance of the United States Forest Service — Jean Lunzer
place the disputed territory under UN surveillance