| Noun | 1. | Military Intelligence Section 5 - the government agency in the United Kingdom that is responsible for internal security and counterintelligence on British territory international intelligence agency - an intelligence agency outside the United States Britain, Great Britain, U.K., UK, United Kingdom, United Kingdom of Great Britain and Northern Ireland - a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom |