Source : Webster's Revised Unabridged Dictionary (1913)

Fallow \Fal"low\, n. [So called from the fallow, or somewhat
   yellow, color of naked ground; or perh. akin to E. felly, n.,
   cf. MHG. valgen to plow up, OHG. felga felly, harrow.]
   1. Plowed land. [Obs.]

            Who . . . pricketh his blind horse over the fallows.
                                                  --Chaucer.

   2. Land that has lain a year or more untilled or unseeded;
      land plowed without being sowed for the season.

            The plowing of fallows is a benefit to land.
                                                  --Mortimer.

   3. The plowing or tilling of land, without sowing it for a
      season; as, summer fallow, properly conducted, has ever
      been found a sure method of destroying weeds.

            Be a complete summer fallow, land is rendered tender
            and mellow. The fallow gives it a better tilth than
            can be given by a fallow crop.        --Sinclair.

   {Fallow crop}, the crop taken from a green fallow. [Eng.]

   {Green fallow}, fallow whereby land is rendered mellow and
      clean from weeds, by cultivating some green crop, as
      turnips, potatoes, etc. [Eng.]