Close observation, especially of a suspected spy or criminal.
‘he found himself put under surveillance by military intelligence’
‘Terrorism has to be fought with knowledge, with surveillance and intelligence.’
‘He says the government cheated him out of money and claims to be under surveillance by the FBI.’
‘We are putting all our sources of surveillance and intelligence together to catch him.’
‘Police have been monitoring the site and using covert surveillance to trap the troublemakers.’
‘The arrests marked the end of weeks of surveillance after a spate of arrests in Europe.’