mark ,  diacritical point ,  diacritical sign ) is an ancillary  glyph  added to a  letter , or basic glyph. The term derives from the  Greek διακριτικός  ( diakritikós , "distinguishing").  Diacritic  is both an  adjective  and a  noun , whereas  diacritical  is only an  adjective . Some diacritical marks, such