A multigraph is a sequence of letters that behaves as a unit and is not the sum of its parts, such as English ⟨ch⟩ or French ⟨eau⟩. The term is infrequently used, as the number of letters is usually specified:

• Digraph
  Digraph (orthography)
  A digraph or digram is a pair of characters used to write one phoneme or a sequence of phonemes that does not correspond to the normal values of the two characters combined...
  
   (two letters, as ⟨ch⟩ or ⟨ea⟩)
• Trigraph
  Trigraph (orthography)
  A trigraph is a group of three letters used to represent a single sound or a combination of sounds that does not correspond to the written letters combined. For example, in the word schilling, the trigraph sch represents the voiceless postalveolar fricative , rather than the consonant cluster...
  
   (three letters, as ⟨tch⟩ or ⟨eau⟩)
• Tetragraph
  Tetragraph
  A tetragraph is a sequence of four letters used to represent a single sound , or a combination of sounds, that do not necessarily correspond to the individual values of the letters. In German, for example, the tetragraph tsch represents the sound of the English digraph ch...
  
   (four letters, as German ⟨tsch⟩)
• Pentagraph
  Pentagraph
  A pentagraph is a sequence of five letters used to represent a single sound , or a combination of sounds, that do not necessarily correspond to the individual values of the letters...
  
   (five letters)
• Hexagraph
  Hexagraph
  A hexagraph is a sequence of six letters used to represent a single sound , or a combination of sounds that do not correspond to the individual values of the letters...
  
   (six letters)
• Heptagraph
  Heptagraph
  A multigraph is a seven-letter sequence of letters that behaves as a unit and is not the sum of its parts, such as the seven-letter German sequence ⟨schtsch⟩, used to transliterate Russian ⟨щ⟩, as in ⟨Borschtsch⟩ for ⟨борщ⟨⟩ "borscht"...
  
   (seven letters)
• Octagraph (eight letters)

Combinations longer than tetragraphs are unusual. The German pentagraph ⟨tzsch⟩ has largely been replaced by ⟨tsch⟩, remaining only in proper name

Proper name

"A proper name [is] a word that answers the purpose of showing what thing it is that we are talking about" writes John Stuart Mill in A System of Logic , "but not of telling anything about it"...

s such as ⟨Poenitzsch⟩. Except for doubled trigraphs like German ⟨schsch⟩, hexagraphs are found only in Irish

Irish orthography

Irish orthography has evolved over many centuries, since Old Irish was first written down in the Latin alphabet in about the 6th century AD. Prior to that, Primitive Irish was written in Ogham...

 vowels, where the outside letters indicate whether the neighboring consonant is "broad

Velarization

Velarization is a secondary articulation of consonants by which the back of the tongue is raised toward the velum during the articulation of the consonant.In the International Phonetic Alphabet, velarization is transcribed by one of three diacritics:...

" or "slender

Palatalization

In linguistics, palatalization , also palatization, may refer to two different processes by which a sound, usually a consonant, comes to be produced with the tongue in a position in the mouth near the palate....

". However, these sequences are not predictable. The hexagraph ⟨oidhea⟩, for example, where the ⟨o⟩ and ⟨a⟩ mark the consonants as broad, represents the same sound (approximately the vowel in English write) as the trigraph ⟨adh⟩, and with the same effect on neighboring consonants.

The seven-letter German sequence ⟨schtsch⟩, used to transliterate Russian ⟨щ⟩, as in ⟨Borschtsch⟩ for ⟨борщ⟨⟩ "borscht

Borscht

Borscht is a soup of Ukrainian origin that is popular in many Eastern and Central European countries. In most of these countries, it is made with beetroot as the main ingredient, giving it a deep reddish-purple color...

", is a sequence of a trigraph ⟨sch⟩ and a tetragraph ⟨tsch⟩ rather than a heptagraph. Likewise, the Juu languages have been claimed to have a heptagraph ⟨dts’kx’⟩, but this is also a sequence, of ⟨dts’⟩ and ⟨kx’⟩.

Beyond the Latin alphabet, Morse code

Morse code

Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

 uses hexagraphs for several punctuation marks, and the dollar sign ⟨$⟩ is a heptagraph, ⟨· · · — · · —⟩. Longer sequences

Prosigns for Morse Code

In Morse code, prosigns or procedural signals are dot/dash sequences that have a special meaning in a transmission: they are a form of control character...

are considered ligatures, and are transcribed as such in the Latin alphabet.