The Collaborative International Dictionary of English v.0.48:

Side \Side\, v. i. [imp. & p. p. Sided; p. pr. & vb. n.
   Siding.]
   1. To lean on one side. [Obs.] --Bacon.
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   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.
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            All side in parties, and begin the attack. --Pope.
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The Collaborative International Dictionary of English v.0.48:

Siding \Sid"ing\, n.
   1. Attaching one's self to a party.
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   2. A side track, as a railroad; a turnout.
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   3. (Carp.) The covering of the outside wall of a frame house,
      whether made of weatherboards, vertical boarding with
      cleats, shingles, or the like.
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   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.
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WordNet (r) 3.0 (2006):

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