Alternative form of security by design

(formal) MI5

plural of security distance

(automotive) the amount of space required between two vehicles on a roadway in order to maintain a safe following distance

The UN Security Council.

Of a device: such that, if it fails, it does so in a way that will cause little or no harm to other devices and personnel.

A blanket that one uses to have a secure feeling or reduced anxiety, usually in the early years of life. / Any object one uses to have a sense of security or reduced anxiety.

(cryptography) Not decodable with all available computer power.

(US, informal) A mother for whom issues of safety and national security are of great importance.

(politics, euphemistic) An army.