Atetragraph, from Greek τετρα (tetra) 'four' and γράφω (gráphō) 'write', is a sequence of four letters used to represent a single sound (phoneme), or a combination of sounds, that do not necessarily correspond to the individual values of the letters.[1] In German, for example, the tetragraphtsch represents the sound of the Englishdigraphch. English does not have tetragraphs in native words (the closest is perhaps the sequence-ough in words likethrough), butchth andphth are true tetragraphs when found initially in words of Greek origin such aschthonic andphthisis.
Phonemes spelled with multiple characters often indicate that either the phoneme or the script is alien to the language. For example, theCyrillic alphabets adapted to theCaucasian languages, which are phonologically very different from Russian, make extensive use of digraphs, trigraphs, and even a tetragraph inKabardian⟨кхъу⟩ for/q͡χʷ/. TheRomanized Popular Alphabet created for theHmong languages includes three tetragraphs:nplh, ntsh, andntxh, which represent complex consonants.
InCyrillic used forlanguages of the Caucasus, there are tetragraphs as doubled digraphs used for 'strong' consonants (typically transcribed in the IPA as geminate), and also labialized homologues of trigraphs.
⟨кхъу⟩ is used inKabardian for[qʷ], the labialized homologue of⟨кхъ⟩[q], in turn unpredictably derived from ejective⟨къ⟩[qʼ].
⟨кӏкӏ⟩ is used inAvar for[kʼː], the 'strong' homologue of⟨кӏ⟩[kʼ], the ejective (⟨ӏ⟩) homologue of⟨к⟩[k]. It is often substituted with⟨кӏ⟩[kʼ].
⟨цӏцӏ⟩ is used in Avar for[tsʼː]. It is often substituted with⟨цӏ⟩[tsʼ].
⟨чӏчӏ⟩ is used in Avar for[tʃʼː]. It is often substituted with⟨чӏ⟩[tʃʼ].
⟨гъӏв⟩ is used inArchi for[ʁʷˤ]
⟨ккъӏ⟩ is used in Archi for[qːʼˤ]
⟨къIв⟩ is used in Archi for[qʼʷˤ]
⟨ллъв⟩ is used in Archi for[ɬːʷ]
⟨ххьI⟩ is used in Archi for[χːˤ]
⟨хъIв⟩ is used in Archi for[qʷˤ]
⟨хьIв⟩ is used in Archi for[χʷˤ]
Inuktitut syllabics has a series of trigraphs forŋ followed by a vowel. For geminateŋŋ, these are form tetragraphs withn:
These are literallynnggi, nnggu, nngga.