What does "mi5" mean?

The domestic intelligence and counter-espionage 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.

What is a synonym for "mi5"?

Common synonyms include: 5, five, five, security service, security service.

Mi5

name

name ·Rare ·Advanced level

Definitions

Proper Noun

1
The domestic intelligence and counter-espionage 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.
"The service aggressively maintained its position until I produced evidence proving it was untrue - including a recording of one of the calls with a senior MI5 officer."

Synonyms

All synonyms

5 five five security service security service

Example

More examples

"The service aggressively maintained its position until I produced evidence proving it was untrue - including a recording of one of the calls with a senior MI5 officer."

Etymology

Abbreviation of Military Intelligence, Section Five.

Related phrases

security service

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.