(military, US, historical, weaponry) Initialism of Missile, Experimental (original project name of the LGM-118 Peacekeeper ICBM).

(Internet) Abbreviation of mail exchanger. / (motorcycling) Abbreviation of motocross. / (philately) on early British stamps, Maltese Cross cancellation mark.

(LGBT) A gender-neutral title used instead of Mr (Mister), Mrs (Mistress), etc.

(medicine) Abbreviation of management.

US and Canada standard form of Mx.

plural of MX

(software, XML) Initialism of M-XML. (Macromedia gives no official meaning for the M in it. It is an XML-based user interface markup language used to develop rich Internet applications.)

Abbreviation of methoxphenidine.

(sports) Abbreviation of motocross grand prix.

(rare) Feminist spelling of man