Source : Webster's Revised Unabridged Dictionary (1913)

Decrement \Dec"re*ment\, n. [L. decrementum, fr. decrescere. See
   {Decrease}.]
   1. The state of becoming gradually less; decrease;
      diminution; waste; loss.

            Twit me with the decrements of my pendants. --Ford.

            Rocks, mountains, and the other elevations of the
            earth suffer a continual decrement.   --Woodward.

   2. The quantity lost by gradual diminution or waste; --
      opposed to {increment}.

   3. (Crystallog.) A name given by Ha["u]y to the successive
      diminution of the layers of molecules, applied to the
      faces of the primitive form, by which he supposed the
      secondary forms to be produced.

   4. (Math.) The quantity by which a variable is diminished.

   {Equal decrement of life}.
      (a) The decrease of life in a group of persons in which
          the assumed law of mortality is such that of a given
          large number of persons, all being now of the same
          age, an equal number shall die each consecutive year.
      (b) The decrease of life in a group of persons in which
          the assumed law of mortality is such that the ratio of
          those dying in a year to those living through the year
          is constant, being independent of the age of the
          persons.

Source : WordNet®

decrement
     n 1: the amount by which something decreases [syn: {decrease}]
          [ant: {increase}]
     2: a process of becoming smaller or shorter [syn: {decrease}]
        [ant: {increase}, {increase}]