Answer: diacritic

AnswerCrossword Clue
DIACRITICDistinctive
diacriticdistinguishing / a mark or sign serving to distinguish different values or sounds of the same letter eg an acute accent
diacriticmark added to a letter to give it a particular phonetic value
diacritica mark, point, or sign added or attached to a letter or character to distinguish it from another of similar form, to give it a particular phonetic value, to indicate stress, etc., as a cedilla, tilde, circumflex, or macron.