Diacritical mark. (n.d.). In YourDictionary. Retrieved from https://www.yourdictionary.com/diacritical-mark
(plural diacritical marks)
(orthography, typography) A symbol in writing used with a letter to indicate a different pronunciation, stress, tone, or meaning, also called "tone marks" when used to indicate tones, e.g. in Vietnamese or pinyin (romanised Mandarin Chinese).