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MI5

[em-ahy-fahyv]
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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
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for mi5

MI5

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

Word Origin and History for mi5

MI5

1939, from abbreviation of Military Intelligence, followed by the department number.

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Online Etymology Dictionary, © 2010 Douglas Harper