Definition - Two or more Glyphs that are members of the same set of glyphs representing a particular grapheme.

Example -
The f in friend and the gh in cough are two of the allographs in the set of glyphs that constitute the grapheme <f>

Etymology -
The word derives from the Greek allos, other + graphos, writing

Oxford English Dictionary -
Its first citation is from 1951:
"We now have allomorph and morpheme, alloseme and sememe, allograph and grapheme."
(R. A. Hall Jun. in Archivum Linguisticum III. 117)

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