allograph

[al-uh-graf, -grahf] /ˈæl əˌgræf, -ˌgrɑf/
noun
1.
Linguistics. a variant form of a grapheme that is in complementary distribution or free variation with another form of the same grapheme, as t and T or n in run and nn in runner; an orthographic contextual variant.
Compare grapheme.
2.
writing or a signature inscribed by one person for another, as distinguished from autograph.
3.
a deed or other legal document not in the writing of any of the persons who are party to it.
Origin
1950-55; allo- + -graph, on the model of allophone
Related forms
allographic
[al-uh-graf-ik] /ˌæl əˈgræf ɪk/ (Show IPA), adjective
Can be confused
allograph, allograft.
British Dictionary definitions for allograph

allograph

/ˈæləˌɡrɑːf/
noun
1.
a document written by a person who is not a party to it
2.
a signature made by one person on behalf of another Compare autograph
3.
(linguistics) any of the written symbols that constitute a single grapheme: m and M are allographs in the Roman alphabet
Derived Forms
allographic (ˌæləˈɡræfɪk) adjective
Word Origin and History for allograph
n.

"writing made by another person," by 1916 (implied in allographic), from allo- + -graph "something written."