grapheme

n. letter or written symbol used to represent a phoneme

In typography, a grapheme is the fundamental unit in written language. Graphemes include alphabetic letters, Chinese characters, numerals, punctuation marks, and all the individual symbols of any of the world's writing systems.In a phonemic orthography, a grapheme corresponds to one phoneme. In spelling systems that are non-phonemic — such as the spellings used most widely for written  English — multiple graphemes may represent a single phoneme. These are called  digraphs (two graphemes for a single phoneme) and trigraphs (three graphemes). For example, the word ship contains four graphemes (s, h, i, and p) but only three phonemes, because sh is a digraph.
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n. grapheme, letter or written symbol used to represent a phoneme

Noun
1. a written symbol that is used to represent speech; "the Greek alphabet has 24 characters"
(synonym) character, graphic symbol
(hypernym) written symbol, printed symbol
(hyponym) allograph