1. [n]  cleaning implement consisting of absorbent material fastened to a handle; for cleaning floors
2. [v]  make a sad face; "mop and mow"
3. [v]  to wash or wipe with or as if with a mop; "Mop the hallway now"; "He mopped her forehead with a towel"

MOP is a 3 letter word that starts with M.

1. \Mop\, n. [See {Mope}.]
   A made-up face; a grimace. ``What mops and mowes it makes!''
   --Beau. & Fl.
   
   

2. \Mop\, v. i.
   To make a wry mouth. [Obs.] --Shak.
   
   

3. \Mop\, n. [CF. W. mop, mopa, Ir. moipal, Gael. moibeal,
   moibean; or OF. mappe a napkin (see {Map}, {Napkin}).]
   1. An implement for washing floors, or the like, made of a
      piece of cloth, or a collection of thrums, or coarse yarn,
      fastened to a handle.
   
   2. A fair where servants are hired. [Prov. Eng.]
   
   3. The young of any animal; also, a young girl; a moppet.
      [Prov. Eng.] --Halliwell.
   
   {Mop head}.
      (a) The end of a mop, to which the thrums or rags are
          fastened.
      (b) A clamp for holding the thrums or rags of a mop.
          [U.S.]
   
   

4. \Mop\, v. t. [imp. & p. p. {Mopped}; p. pr. & vb. n.
   {Mopping}.]
   To rub or wipe with a mop, or as with a mop; as, to mop a
   floor; to mop one's face with a handkerchief.