Source : Webster's Revised Unabridged Dictionary (1913)

Magnitude \Mag"ni*tude\, n. [L. magnitudo, from magnus great.
   See {Master}, and cf. {Maxim}.]
   1. Extent of dimensions; size; -- applied to things that have
      length, breath, and thickness.

            Conceive those particles of bodies to be so disposed
            amongst themselves, that the intervals of empty
            spaces between them may be equal in magnitude to
            them all.                             --Sir I.
                                                  Newton.

   2. (Geom.) That which has one or more of the three
      dimensions, length, breadth, and thickness.

   3. Anything of which greater or less can be predicated, as
      time, weight, force, and the like.

Source : WordNet®

magnitude
     n 1: the property of relative size or extent; "they tried to
          predict the magnitude of the explosion"
     2: a number assigned to the ratio of two quantities; two
        quantities are of the same order of magnitude if one is
        less than 10 times as large as the other; the number of
        magnitudes that the quantities differ is specified to
        within a power of 10 [syn: {order of magnitude}]
     3: relative importance; "a problem of the first magnitude"