• MI5

    Origin

    Originally an abbreviation for Military Intelligence, division five.

    Full definition of MI5

    Proper noun

    MI5

    (plural MI5s)
    1. The domestic intelligence agency of the United Kingdom, which operates in secret and whose primary function is to spy on terrorist organizations and others viewed as a threat to British national security. Formally known as the Security Service.

    Synonyms

    Related terms

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