A diacritic /daɪ.əˈkrɪtɪk/ – also diacritical mark, diacritical point, or diacritical sign – is a glyph added to a letter, or basic glyph.The term derives from the Greek διακριτικός (diakritikos, diakritikós), distinguishing which is composed of the Ancient greek (διά, dia) diá through (and κρίνω krinein, krínein or). krino kríno to separate diacritic /daɪ.əˈkrɪtɪk/ – also diacritical mark, diacritical point, or diacritical sign – is a glyph added to a letter, or basic glyph.