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.]
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            They put all the little plate they had in the
            lumber, which is pawning it, till the ships came.
                                                  --Lady Murray.
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   2. Old or refuse household stuff; things cumbrous, or bulky
      and useless, or of small value.
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   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.]
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   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:

Dimension \Di*men"sion\, n. [L. dimensio, fr. dimensus, p. p. of
   dimetiri to measure out; di- = dis- + metiri to measure: cf.
   F. dimension. See Measure.]
   1. Measure in a single line, as length, breadth, height,
      thickness, or circumference; extension; measurement; --
      usually, in the plural, measure in length and breadth, or
      in length, breadth, and thickness; extent; size; as, the
      dimensions of a room, or of a ship; the dimensions of a
      farm, of a kingdom.
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            Gentlemen of more than ordinary dimensions. --W.
                                                  Irving.
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   Space of dimension, extension that has length but no
      breadth or thickness; a straight or curved line.

   Space of two dimensions, extension which has length and
      breadth, but no thickness; a plane or curved surface.

   Space of three dimensions, extension which has length,
      breadth, and thickness; a solid.

   Space of four dimensions, as imaginary kind of extension,
      which is assumed to have length, breadth, thickness, and
      also a fourth imaginary dimension. Space of five or six,
      or more dimensions is also sometimes assumed in
      mathematics.
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   2. Extent; reach; scope; importance; as, a project of large
      dimensions.
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   3. (Math.) The degree of manifoldness of a quantity; as, time
      is quantity having one dimension; volume has three
      dimensions, relative to extension.
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   4. (Alg.) A literal factor, as numbered in characterizing a
      term. The term dimensions forms with the cardinal numbers
      a phrase equivalent to degree with the ordinal; thus,
      a^2b^2c is a term of five dimensions, or of the fifth
      degree.
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   5. pl. (Phys.) The manifoldness with which the fundamental
      units of time, length, and mass are involved in
      determining the units of other physical quantities.

   Note: Thus, since the unit of velocity varies directly as the
         unit of length and inversely as the unit of time, the
         dimensions of velocity are said to be length [divby]
         time; the dimensions of work are mass [times]
         (length)^2 [divby] (time)^2; the dimensions of
         density are mass [divby] (length)^3.

   Dimensional lumber, Dimension lumber, Dimension
   scantling, or Dimension stock (Carp.), lumber for
      building, etc., cut to the sizes usually in demand, or to
      special sizes as ordered.

   Dimension stone, stone delivered from the quarry rough, but
      brought to such sizes as are requisite for cutting to
      dimensions given.
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