M9 n.
(UK black) online term for a very good friend, even more so than a M8 (mate).
 | hubpages.com ‘Roadman Slang 10 Jan. 🌐 M9 - used online and never said out loud, ‘m9’ takes the meaning of being ‘even better than m8’. It's a comical way to let someone know that you consider them a good friend. |