B1[U]protection of a person, building, organization, or country against threats such as crime or attacks by foreign countries: The station was closed for two hours because of a security alert.30 demonstrators were killed in clashes with the security forces over the weekend.The tighter security measures/precautions include video cameras in the city centre.The students were deported because they posed a threat to national security.The proposed national identity card system would help to tighten security against fraud.The most dangerous criminals are held in maximum-security prisons (= prisons that are as difficult as possible to escape from).Protection and protectorsEnvironmental issues›[U, + sing/pl verb]the group of people responsible for protecting a building: You'll need to notify security if you want to work late in the office.Protection and protectorsEnvironmental issues