The Collaborative International Dictionary of English v.0.48:

Elongation \E`lon*ga"tion\ (?; 277), n. [LL. elongatio: cf. F.
   ['e]longation.]
   1. The act of lengthening, or the state of being lengthened;
      protraction; extension. "Elongation of the fibers."
      --Arbuthnot.
      [1913 Webster]

   2. That which lengthens out; continuation.
      [1913 Webster]

            May not the mountains of Westmoreland and Cumberland
            be considered as elongations of these two chains?
                                                  --Pinkerton.
      [1913 Webster]

   3. Removal to a distance; withdrawal; a being at a distance;
      distance.
      [1913 Webster]

            The distant points in the celestial expanse appear
            to the eye in so small a degree of elongation from
            one another, as bears no proportion to what is real.
                                                  --Glanvill.
      [1913 Webster]

   4. (Astron.) The angular distance of a planet from the sun;
      as, the elongation of Venus or Mercury.
      [1913 Webster]

WordNet (r) 3.0 (2006):

elongation
    n 1: the quality of being elongated
    2: an addition to the length of something [syn: elongation,
       extension]
    3: the act of lengthening something