Gh is a digraph found in many languages.
In English, (gh) historically represented pronounced as /[x]/ (the voiceless velar fricative, as in the Scottish Gaelic word), and still does in lough and certain other Hiberno-English words, especially proper nouns. In the dominant dialects of modern English, (gh) is almost always either silent or pronounced pronounced as //f// (see Ough). It is thought that before disappearing, the sound became partially or completely voiced to pronounced as /[ɣx]/ or pronounced as /[ɣ]/, which would explain the new spelling — Old English used a simple (h) — and the diphthongization of any preceding vowel.
Alexander John Ellis reported it being pronounced as pronounced as /[x]/ on the Yorkshire-Lancashire border and close to the Scottish border in the late nineteenth century.[1]
It is also occasionally pronounced pronounced as /[ə]/, such as in Edinburgh as well as pronounced as /[θ]/ in Keighley.
When gh occurs at the beginning of a word in English, it is pronounced pronounced as //ɡ// as in "ghost", "ghastly", "ghoul", "ghetto", "ghee" etc. In this context, it does not derive from a former pronounced as //x//.
American Literary Braille has a dedicated cell pattern for the digraph (gh) (dots 126, ⠣).
In Middle Dutch, (gh) was often used to represent pronounced as //ɣ// (the voiced velar fricative) before (e), (i), and (y). This usage survives in place names such as Ghent.
The spelling of English word ghost with a (gh) (from Middle English) was likely influenced by the Middle Dutch spelling Dutch, Middle (ca.1050-1350);: gheest (Modern Dutch).
In Italian and Romanian, (gh) represents pronounced as //ɡ// (the voiced velar plosive) before (e) and (i). In Esperanto orthography, (gh) (or (gx)) can be used when the (ĝ) is missing, which represents pronounced as /link/. In Galician, it is often used to represent the pronunciation of gheada.
In Irish, (gh) represents pronounced as //ɣ// (the voiced velar fricative) and pronounced as //j// (the voiced palatal approximant). Word-initially it represents the lenition of (g), for example Irish: mo ghiall in Irish pronounced as /mˠə ˈjiəl̪ˠ/ 'my jaw' (compare Irish: giall in Irish pronounced as /ˈɟiəl̪ˠ/ 'jaw').
In Juǀʼhoan, it's used for the prevoiced aspirated velar plosive pronounced as //ɡ͡kʰ//.
In the Malay and Indonesian alphabet, (gh) is used to represent the voiced velar fricative (pronounced as //ɣ//) in Arabic origin words.
The Maltese language has a related digraph, (għ). It is considered a single letter, called għajn (the same word for eye and spring, named for the corresponding Arabic letter ʿayn). It is usually silent, but it is necessary to be included because it changes the pronunciation of neighbouring letters, usually lengthening the succeeding vowels. At the end of a word, when not substituted by an apostrophe, it is pronounced pronounced as /link/. Its function is thus not unlike modern English gh, except that the English version comes after vowels rather than before like Maltese għ (għajn would come out something like ighn if spelled as in English).
In the Roman Swahili alphabet, (gh) is used to represent the voiced velar fricative (pronounced as //ɣ//) in Arabic origin words.
In Canadian Tlingit (gh) represents pronounced as //q//, which in Alaska is written (ǥ).
In Daighi tongiong pingim, (gh) represents pronounced as //ɡ// (the voiced velar stop) before (a), (e), (i), (o), and (u).
In Uyghur Latin script, gh represents pronounced as /link/.
In Vietnamese alphabet, (gh) represents pronounced as //ɣ// before (e), (ê), (i).
In the romanization of various languages, (gh) usually represents the voiced velar fricative (pronounced as //ɣ//). Like (kh) pronounced as //x//, (gh) may also be pharyngealized, as in several Caucasian and Native American languages.In transcriptions of Indo-Aryan languages such as Sanskrit and Hindi, as well as their ancestor, Proto-Indo-European, (gh) represents a voiced velar aspirated plosive pronounced as //ɡʱ// (often referred to as a breathy or murmured voiced velar plosive).
The Ukrainian National transliteration system uses (gh) to avoid occurrence of another digraph, usually (zh) which is used for another type of phoneme. Such as the word "pack" (a group of animals) in Ukrainian would be Romanized as zghraia (Ukrainian: зграя) rather than zhraia, which could be misconstrued to intend Ukrainian: *жрая. The Ukrainian transliteration standard DSTU 9112:2021 (based on) uses (gh) to represent common Ukrainian letter г (the voiced glottal fricative pronounced as //ɦ//).