Such a key is sometimes referred to as a dead key, as it produces no output of its own but modifies the output of the key pressed after it.
In modern Microsoft Windows and Linux operating systems, the keyboard layouts US International and UK International feature dead keys that allow one to type Latin letters with the acute, grave, circumflex, diæresis, tilde, and cedilla found in Western European languages (specifically, those combinations found in the ISO Latin-1 character set) directly: ¨ e gives ë, ~ o gives õ, etc.
Examples are the diaereses in the borrowed French words naïve and Noël, which show that the vowel with the diaeresis mark is pronounced separately from the preceding vowel; the acute and grave accents, which can indicate that a final vowel is to be pronounced, as in saké and poetic breathèd; and the cedilla under the "c" in the borrowed French word façade, which shows it is pronounced .
In Gaelic type, a dot over a consonant indicates lenition of the consonant in question.
With the advent of Roman type it was reduced to the round dot we have today.
Diacritic is primarily an adjective, though sometimes used as a noun, whereas diacritical is only ever an adjective.
Some diacritical marks, such as the acute ( ´ ) and grave ( ` ), are often called accents.
In other alphabetic systems, diacritical marks may perform other functions.
Vowel pointing systems, namely the Arabic harakat ( ), which, respectively, mark abbreviations or acronyms, and Greek diacritical marks, which showed that letters of the alphabet were being used as numerals.