DIGRAPH. A term in ORTHOGRAPHY for two LETTERS that represent one sound, such as th in this and sh in ashes. If three letters together represent a single sound, they constitute a trigraph, such as tch in catch and sch in schmaltz. When letters form digraphs, they surrender their independent sound values so as to stand as a group for a single phoneme, usually because an alphabet has no letter to serve that purpose. In such cases, there may be some phonetic motivation in the combination (sh, dg roughly suggesting the sounds in dash and dodge), though this may have vanished as pronunciation has changed (for example, the gh in tough and through). Sometimes letters that happen to come together may look like (and be mistaken for) digraphs: for example, the t, h in posthumous being interpreted as the th in asthma. Because English has more phonemes than letters, digraphs are used to represent sounds for which no original Roman letter would serve: for example, the initial sounds in three and this and the final sounds in rich and ridge. There is a greater degree of consistency in English in the use of consonant digraphs and trigraphs than in vowel digraphs.

Consonant digraphs

Most English consonant digraphs consist of a single letter followed by h, modelled on the Latin digraphs ch, ph, th used to transcribe the Greek letters chi, phi, and theta. Consonant digraphs include: ch as in chair, charisma, and loch; sh as in shout; th as in three and these; wh as in whale; ph as in philosophy; gh as in tough and daughter; ng as in longer and singer; ck as in track; dg as in judge. Although zh is not a conventional digraph in English, occurring mainly in loans from Russian (Brezhnev), it is well understood and is sometimes used to give a spelling pronunciation of a word (measure as ‘mezher’).

Vowel digraphs

Because the vowel sounds of English greatly outnumber the symbols available, digraphs are widely used to represent them. A few are fairly regular, such as ai in fail, pain, maintain, but most can represent several vowels (as with ea in bead, bread, break, hear, hearse, heart) and many vowels can be represented by a variety of digraphs (especially if ‘magic’ e as in fate, eve, wise, rote, mute is counted as the second element in alternative digraphs to those in wait, eat, flies, oat, root). Most problematic is the spelling of the long e sound, as in the patterns be, bee, eve, leave, sleeve, deceive, believe, (BrE) anaemia, (BrE) foetus, routine. Some digraphs representing a vowel combine vowel and consonant letters (sight, sign, indict), while others vary within the same root (speak/speech, high/height). In addition, vowel digraphs are well known for their use in a number of highly irregular, sometimes unique spellings, such as quay, key, people, leopard, broad, brooch, blood, build.

The digraphs Æ and Œ

The LIGATURE digraph æ in Ælfric, Cæsar, encyclopædia was originally used in Latin and adopted by Old English for the vowel in hat (hæt), often referred to as ASH. It has been used in English, under the influence of Latin, to represent Greek ai as in Æschylus, Æsop, anæmia, hæmorrhage, now commonly Aeschlus, Aesop, and BrE anaemia, haemorrhage. The AmE practice of simplifying ae to e is becoming general, as in anemia, hemorrhage, encyclopedia, medieval, but not *Eschylus, *Esop. The Latin ligature digraph œrepresents Greek oi as in Œdipus, amœba, now commonly Oedipus and BrE amoeba, foetus. The AmE practice of simplifying oe to e is becoming general, as in ameba, fetus, but not *Edipus. In some words, the digraph (with or without the ligature) has long since vanished: for example, older oeconomy is now universally economy, and ecology has never been spelt oecology. See DIPHTHONG, SPELLING, WRITING, and A, C, E, G, H, I, K, O, P, R, S, T, W.

di·graph / ˈdīˌgraf/ • n. a combination of two letters representing one sound, as in ph and ey. ∎ Printing a character consisting of two joined letters; a ligature.DERIVATIVES: di·graph·ic / dīˈgrafik/ adj.

digraph group of two letters representing one sound. XVIII. f. Gr. DI- 2 + graphḗ writing.

digraph Short for directed graph. See graph.

digraph (ˈdaɪgræf) Computing directed graph