A multigraph (or pleograph) 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: Combinations longer than tetragraphs are unusual.
Except for doubled trigraphs like German ⟨schsch⟩, hexagraphs are found only in Irish vowels, where the outside letters indicate whether the neighboring consonant is "broad" or "slender".
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 uses hexagraphs for several punctuation marks, and the dollar sign ⟨$⟩ is a heptagraph, ⟨· · · — · · —⟩.