Source : Webster's Revised Unabridged Dictionary (1913)

Diacritic \Di`a*crit"ic\, Diacritical \Di`a*crit"ic*al\, a. [Gr.
   ?, fr. ? to separate, distinguish; dia` through + ? to
   separate. See {Critic}.]
   That separates or distinguishes; -- applied to points or
   marks used to distinguish letters of similar form, or
   different sounds of the same letter, as, [=a], [a^], ["a],
   [=o], [o^], etc. ``Diacritical points.'' --Sir W. Jones.

         A glance at this typography will reveal great
         difficulties, which diacritical marks necessarily throw
         in the way of both printer and writer.   --A. J. Ellis.

Source : WordNet®

diacritic
     adj : capable of distinguishing; "students having superior
           diacritic powers"; "the diacritic elements in culture"-
           S.F.Nadel [syn: {diacritical}]

diacritic
     n : a mark added to a letter to indicate a special pronunciation
         [syn: {diacritical mark}]