Source : Webster's Revised Unabridged Dictionary (1913)

Side \Side\, v. i. [imp. & p. p. {Sided}; p. pr.& vb. n.
   {Siding}.]
   1. To lean on one side. [Obs.] --Bacon.

   2. To embrace the opinions of one party, or engage in its
      interest, in opposition to another party; to take sides;
      as, to side with the ministerial party.

            All side in parties, and begin the attack. --Pope.

Siding \Sid"ing\, n.
   1. Attaching one's self to a party.

   2. A side track, as a railroad; a turnout.

   3. (Carp.) The covering of the outside wall of a frame house,
      whether made of weatherboards, vertical boarding with
      cleats, shingles, or the like.

   4. (Shipbuilding) The thickness of a rib or timber, measured,
      at right angles with its side, across the curved edge; as,
      a timber having a siding of ten inches.

Source : WordNet®

siding
     n 1: a short stretch of railroad track used to store rolling
          stock or enable trains on the same line to pass [syn: {railroad
          siding}, {turnout}, {sidetrack}]
     2: material applied to the outside of a building to make it
        weatherproof