diacritic

This term is primarily used in linguistics, typography, and philology. It describes a functional addition to a base character rather than a standalone letter. While often used interchangeably with "accent" in casual conversation, "diacritic" is the precise technical term that encompasses a wider range of marks, including cedillas, tildes, and umlauts, regardless of whether they indicate pitch, stress, or a change in consonant quality.

In a professional or academic register, using "diacritic" signals a focus on the orthographic system of a language. When used as an adjective, it typically modifies nouns like "mark," "sign," or "system" to specify the nature of the typographic element being discussed.