Abbreviation of Missus or Mistress (“used before an adult woman's name or surname, used for any high-status woman without regard to marital status until the 1800s, after which it began to be reserved for married, divorced and widowed women and used with their married surnames”)

US and Canada standard form of Mrs.

Initialism of Materials Research Society. / Initialism of Melbourne Rectangular Stadium.

Initialism of magnetic resonance spectroscopy. / Initialism of mandibular repositioning splint. / Initialism of marginal rate of substitution. / Initialism of metabolic risk score.

Alternative form of Mister Right

(informal) The head of a crime syndicate, a high-ranking criminal.

Alternative form of Mr. Big

plural of Mr Big

(US, politics) Nonstandard form of Mr. President. / Alternative form of Mister President

Alternative form of MRDD