A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter or to a basic glyph. The term derives from the Ancient Greek διακριτικός (diakritikós, "distinguishing"), from διακρίνω (diakrínō, "to distinguish"). The word diacritic is a noun, though it is sometimes used in an attributive sense, whereas diacritical is only an adjective. Some diacritics, such as the acute ⟨ó⟩, grave ⟨ò⟩, and circumflex ⟨ô⟩ (all shown above an 'o'), are often called accents. Diacritics may appear above or below a letter or in some other position such as within the letter or between two letters.
The main use of diacritics in Latin script is to change the sound-values of the letters to which they are added. Historically, English has used the diaeresis diacritic to indicate the correct pronunciation of ambiguous words, such as "coöperate", without which the <oo> letter sequence could be misinterpreted to be pronounced /ˈkuːpəreɪt/. Other examples are the acute and grave accents, which can indicate that a vowel is to be pronounced differently than is normal in that position, for example not reduced to /ə/ or silent as in the case of the two uses of the letter e in the noun résumé (as opposed to the verb resume) and the help sometimes provided in the pronunciation of some words such as doggèd, learnèd, blessèd, and especially words pronounced differently than normal in poetry (for example movèd, breathèd).
