Source : Webster's Revised Unabridged Dictionary (1913)

Truncation \Trun*ca"tion\, n. [L. truncatio.]
   1. The act of truncating, lopping, or cutting off.

   2. The state of being truncated.

   3. (Min.) The replacement of an edge or solid angle by a
      plane, especially when the plane is equally inclined to
      the adjoining faces.

Source : WordNet®

truncation
     n 1: the property of being truncated or short [syn: {shortness}]
     2: the replacement of an edge or solid angle (as in cutting a
        gemstone) by a plane (especially by a plane that is
        equally inclined to the adjacent faces)
     3: the act of cutting short; "it is an obvious truncation of
        the verse"; "they were sentenced to a truncation of their
        limbs"