Source : Webster's Revised Unabridged Dictionary (1913)

Valley \Val"ley\, n.; pl. {Valleys}. [OE. vale, valeie, OF.
   val['e]e, valede, F. vall['e]e, LL. vallata, L. vallis,
   valles. See {Vale}.]
   1. The space inclosed between ranges of hills or mountains;
      the strip of land at the bottom of the depressions
      intersecting a country, including usually the bed of a
      stream, with frequently broad alluvial plains on one or
      both sides of the stream. Also used figuratively.

            The valley of the shadow of death.    --Ps. xxiii.
                                                  4.

            Sweet interchange Of hill and valley, rivers, woods,
            and plains.                           --Milton.

   Note: Deep and narrow valleys with abrupt sides are usually
         the results of erosion by water, and are called
         {gorges}, {ravines}, {ca[~n]ons}, {gulches}, etc.

   2. (Arch.)
      (a) The place of meeting of two slopes of a roof, which
          have their plates running in different directions, and
          form on the plan a re["e]ntrant angle.
      (b) The depression formed by the meeting of two slopes on
          a flat roof.

   {Valley board} (Arch.), a board for the reception of the lead
      gutter in the valley of a roof. The valley board and lead
      gutter are not usual in the United States.

   {Valley rafter}, or {Valley piece} (Arch.), the rafter which
      supports the valley.

   {Valley roof} (Arch.), a roof having one or more valleys. See
      {Valley}, 2, above.

Source : WordNet®

valley
     n : a long depression in the surface of the land that usually
         contains a river [syn: {vale}]