The Collaborative International Dictionary of English v.0.48:

Lawn \Lawn\ (l[add]n), n. [OE. laund, launde, F. lande heath,
   moor; of Celtic origin; cf. W. llan an open, clear place,
   llawnt a smooth rising hill, lawn, Armor. lann or lan
   territory, country, lann a prickly plant, pl. lannou heath,
   moor.]
   1. An open space between woods. --Milton.
      [1913 Webster]

            "Orchard lawns and bowery hollows."   --Tennyson.
      [1913 Webster]

   2. Ground (generally in front of or around a house) covered
      with grass kept closely mown.
      [1913 Webster]

   Lawn mower, a machine for clipping the short grass of
      lawns.

   Lawn tennis, a variety of the game of tennis, played in the
      open air, sometimes upon a lawn, instead of in a tennis
      court. See Tennis.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lawn mower
    n 1: garden tool for mowing grass on lawns [syn: lawn mower,
         mower]