Letter (alphabet)

A letter is a grapheme (written character) in an alphabetic system of writing, such as the Greek alphabet and its descendants. Letters also appear in abjads and abugidas (variants of alphabets in which vowel marking is secondary or absent). Letters broadly denote phonemes in the spoken form of the language, although there is rarely a consistent exact correspondence between letters and phonemes.

Written signs in other writing systems are best called syllabograms (which denote a syllable) or logograms (which denote a word or phrase).

"Letter," borrowed from Old French lettre, entered Middle English around AD 1200, eventually displacing the native English term bocstaf (i.e. ). Letter derives from Latin , which may have derived, via Etruscan, from the Greek "διφθέρα" (writing tablet). The Middle English plural lettres could refer to an epistle or written document, reflecting the use of the Latin plural litteræ. Use of the singular letter to refer to a written document emerged in the 14th century.

As symbols that denote segmental speech, letters are associated with phonetics. In a purely phonemic alphabet, a single phoneme is denoted by a single letter, but in history and practice letters often denote more than one phoneme. A pair of letters designating a single phoneme is called a digraph. Examples of digraphs in English include "ch", "sh" and "th". A phoneme can also be represented by three letters, called a trigraph. An example is the combination "sch" in German.

A letter may also be associated with more than one phoneme, with the phoneme depending on the surrounding letters or etymology of the word. As an example of positional effects, the Spanish letter c is pronounced [k] before a, o, or u (e.g. cantar, corto, cuidado), but is pronounced [θ] before e or i (e.g. centimo, ciudad).

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