Beretta 92FS 9mm semiautomatic pistol as adopted by the armed forces of the United States. Probably the sexiest gun of any type ever made.
My M4 burped on a whole shitload of sand, so I whipped out my M9 and continued engaging the bad guys with it.
M9 by Lior Bar-On June 13, 2004
M9 by BïPolarBear July 5, 2016
When a newb tries to be a smart arse when calling you mate abbreviated as m9 instead of m8 just to piss you off. More commonly when playing an FPS such as Battlefield or CoD.
m9 by RoboticRansom May 11, 2016
Equivalent to m8, which is obviously short for "mate" mostly used in by immature 12 year olds or in dank mlg montages.
M9 by Dank_Shrekmaster69 November 3, 2016