/sɜ:'veɪləns; sɚ`veləns/
n [U] careful watch kept on sb suspected of doing wrong （对涉嫌者的）监视
*The police are keeping the suspects under round-the-clock surveillance. 警方对疑犯昼夜监视.

n[U]
[Date: 1800-1900; Language: French;Origin: surveiller 'to watch over', from sur- ( SURCHARGE) + veiller 'to watch' (from Latin vigil; VIGIL)]
when the police, army, etc watch a person or place carefully because they may be connected with criminal activities
surveillance of
　24-hour surveillance of the building
under surveillance
　They were under constant close surveillance day and night.
　The suspects were kept under surveillance .
　electronic surveillance equipment
when one country watches the military activities of another country to see what they are planning to do
　a surveillance mission
　surveillance aircraft
when doctors, health departments etc watch an ill person or watch the development of a disease in a population
under surveillance
　Diane was placed under psychiatric surveillance.