The Collaborative International Dictionary of English v.0.48:

Rail \Rail\, n. [Akin to LG. & Sw. regel bar, bolt, G. riegel a
   rail, bar, or bolt, OHG. rigil, rigel, bar, bolt, and
   possibly to E. row a line.]
   1. A bar of timber or metal, usually horizontal or nearly so,
      extending from one post or support to another, as in
      fences, balustrades, staircases, etc.
      [1913 Webster]

   2. (Arch.) A horizontal piece in a frame or paneling. See
      Illust. of Style.
      [1913 Webster]

   3. (Railroad) A bar of steel or iron, forming part of the
      track on which the wheels roll. It is usually shaped with
      reference to vertical strength, and is held in place by
      chairs, splices, etc.
      [1913 Webster]

   4. (Naut.)
      (a) The stout, narrow plank that forms the top of the
          bulwarks.
      (b) The light, fencelike structures of wood or metal at
          the break of the deck, and elsewhere where such
          protection is needed.
          [1913 Webster]

   5. A railroad as a means of transportation; as, to go by
      rail; a place not accesible by rail.
      [Webster 1913 Suppl.]

   6. a railing.
      [PJC]

   Rail fence. See under Fence.

   Rail guard.
      (a) A device attached to the front of a locomotive on each
          side for clearing the rail of obstructions.
      (b) A guard rail. See under Guard.

   Rail joint (Railroad), a splice connecting the adjacent
      ends of rails, in distinction from a chair, which is
      merely a seat. The two devices are sometimes united. Among
      several hundred varieties, the fish joint is standard. See
      Fish joint, under Fish.

   Rail train (Iron & Steel Manuf.), a train of rolls in a
      rolling mill, for making rails for railroads from blooms
      or billets.
      [1913 Webster]