[ em-ahy-fahyv ]

noun(in Great Britain)
  1. the government's security and counterespionage service that works in liaison with Scotland Yard's Special Branch.

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Origin of MI5

M(ilitary)I(ntelligence, Section) 5

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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

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British Dictionary definitions for MI5


abbreviation for
  1. Military Intelligence, section five; a former official and present-day popular name for the counterintelligence agency of the British Government

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012