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: Webster's Revised Unabridged Dictionary (1913)