1. [n]  the Gaelic language formerly spoken on the Isle of Man
2. [adj]  of or relating to the Isle of Man or its inhabitants or their language; "the Manx fishing industry"; "there are few Manx speakers alive today"

MANX is a 4 letter word that starts with M.

1. \Manx\, a.
   Of or pertaining to the Isle of Man, or its inhabitants; as,
   the Manx language.
   
   {Manx cat} (Zo["o]l.), a breed of domestic cats having a
      rudimentary tail, containing only about three vertebrae.
   
   
   {Manx shearwater} (Zo["o]l.), an oceanic bird ({Puffinus
      anglorum}, or {P. puffinus}), called also {Manx petrel},
      {Manx puffin}. It was formerly abundant in the Isle of
      Man.
   
   

2. \Manx\, n.
   The language of the inhabitants of the Isle of Man, a dialect
   of the Celtic.