allograph
noun
al·lo·graph ˈa-lə-ˌgraf 
1
: a letter of an alphabet in a particular shape (such as A or a)
2
: a letter or combination of letters that is one of several ways of representing one phoneme (such as pp in hopping representing the phoneme \\p\\)
allographic
ˌa-lə-ˈgra-fik
adjective 
Word History
Etymology
allo- + -graph, (in grapheme), on the model of allomorph : morpheme, allophone : phoneme
First Known Use
1951, in the meaning defined at sense 1