Is there a word or short term for words that have more than one valid spelling (not corresponding to any difference in meaning or pronunciation)? The different spellings can be described as "spelling variants", but I'm looking for a word to describe the words themselves. I don't consider the term "homophones" (or the more specific "heterographic homophones") to be applicable because I understand it to refer to words that have different meanings.

A noun would be ideal ("*Ax(e)* is a(n) __") but an adjective that can modify a noun like *word* would be OK too ("*Ax(e)* is a(n) __ word"). To be clear, in this sentence I am using *ax(e)* to refer to the word itself, not to either of its two spelling variants.