The Collaborative International Dictionary of English v.0.48:

Lumber \Lum"ber\, n. [Prob. fr. Lombard, the Lombards being the
   money lenders and pawnbrokers of the Middle Ages. A lumber
   room was, according to Trench, originally a Lombard room, or
   room where the Lombard pawnbroker stored his pledges. See
   Lombard.]
   1. A pawnbroker's shop, or room for storing articles put in
      pawn; hence, a pledge, or pawn. [Obs.]
      [1913 Webster]

            They put all the little plate they had in the
            lumber, which is pawning it, till the ships came.
                                                  --Lady Murray.
      [1913 Webster]

   2. Old or refuse household stuff; things cumbrous, or bulky
      and useless, or of small value.
      [1913 Webster]

   3. Timber sawed or split into the form of beams, joists,
      boards, planks, staves, hoops, etc.; esp., that which is
      smaller than heavy timber. [U.S.]
      [1913 Webster]

   Lumber kiln, a room in which timber or lumber is dried by
      artificial heat. [U.S.]

   Lumber room, a room in which unused furniture or other
      lumber is kept. [U.S.]

   Lumber wagon, a heavy rough wagon, without springs, used
      for general farmwork, etc.

   dimensional lumber, lumber, usually of pine, which is sold
      as beams or planks having a specified nominal
      cross-section, usually in inches, such a two-by-four,
      two-by-six, four-by-four, etc.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Lumber \Lum"ber\, v. t. [imp. & p. p. Lumbered; p. pr. & vb.
   n. Lumbering.]
   1. To heap together in disorder. " Stuff lumbered together."
      --Rymer.
      [1913 Webster]

   2. To fill or encumber with lumber; as, to lumber up a room.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lumber \Lum"ber\, v. i.
   1. To move heavily, as if burdened.
      [1913 Webster]

   2. [Cf. dial. Sw. lomra to resound.] To make a sound as if
      moving heavily or clumsily; to rumble. --Cowper.
      [1913 Webster]

   3. To cut logs in the forest, or prepare timber for market.
      [U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

lumber
    n 1: the wood of trees cut and prepared for use as building
         material [syn: lumber, timber]
    2: an implement used in baseball by the batter [syn: baseball
       bat, lumber]
    v 1: move heavily or clumsily; "The heavy man lumbered across
         the room" [syn: lumber, pound]
    2: cut lumber, as in woods and forests [syn: log, lumber]