;Maunsell:Richard Maunsell, Chief Mechanical Engineer (CME) of the South Eastern and Chatham Railway from 1913-1923, and of the Southern Railway 1923-1937.
;McIntosh:John Farquharson McIntosh, Chief Mechanical Engineer (CME) of the Caledonian Railway 1895-1914
;MEWP:Mobile elevating work platform
;Mica:GWR telegraphic code signifying a meat van
;Mink:GWR telegraphic code signifying a covered goods van