/ sɜːˈveɪləns; NAmE sɜːrˈv-/ noun
[ U ] the act of carefully watching a person suspected of a crime or a place where a crime may be committed
SYN observation :
The police are keeping the suspects under constant surveillance .
surveillance cameras / equipment
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WORD ORIGIN
early 19th cent.: from French , from sur- over + veiller watch (from Latin vigilare keep watch).