m m /ˈɛm/

adjective

1. Denoting a quantity consisting of 1,000 items or units  ( k , m , one thousand , 1000 , thousand )
   denoting a quantity consisting of 1,000 items or units
     The charity raised a thousand dollars for the cause.
   The charity raised a thousand dollars for the cause.
   

noun

1. () The basic unit of length adopted under the Système International d'Unités (approximately 1.094 yards)  ( metre [Canadian, British] , m , meter [American] )
   the basic unit of length adopted under the Système International d'Unités (approximately 1.094 yards)
    The room is 4 metres wide and 6 metres long
   The room is 4 metres wide and 6 metres long
   
   

 M

1. () Concentration measured by the number of moles of solute per liter of solution  ( molar concentration , molarity , M )
   concentration measured by the number of moles of solute per liter of solution
   
2. The 13th letter of the Roman alphabet  ( M )
   the 13th letter of the Roman alphabet
   
3. A unit of information equal to 1024 kibibytes or 2^20 (1,048,576) bytes  ( M , MB , mebibyte , megabyte , MiB )
   a unit of information equal to 1024 kibibytes or 2^20 (1,048,576) bytes
   
4. A unit of information equal to 1000 kilobytes or 10^6 (1,000,000) bytes  ( M , MB , megabyte )
   a unit of information equal to 1000 kilobytes or 10^6 (1,000,000) bytes
   
5. The cardinal number that is the product of 10 and 100  ( 1000 , chiliad , G , grand , K , M , one thousand , thou , yard , thousand )
   the cardinal number that is the product of 10 and 100
    There are one thousand meters in a kilometer
   There are one thousand meters in a kilometer