MEZZOTINT is a 9 letter word that starts with M.

1. \Mez"zo*tint\, n. [Cf. F. mezzo-tinto.]
   A manner of engraving on copper or steel by drawing upon a
   surface previously roughened, and then removing the roughness
   in places by scraping, burnishing, etc., so as to produce the
   requisite light and shade. Also, an engraving so produced.
   
   

2. \Mez"zo*tint\, v. t.
   To engrave in mezzotint.