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.
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.
This varies from language to language, and may vary from case to case within a language.
In orthography and collation, a letter modified by a diacritic may be treated either as a new, distinct letter or as a letter–diacritic combination.
It first appeared in the 11th century in the sequence ii (as in ingeníí), then spread to i adjacent to m, n, u, and finally to all lowercase i's.
The j, originally a variant of i, inherited the tittle.
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.