Not sure about what purity and etymology have to do with one another. I am reminded of a great quotation from the early days of the Internet:
The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and riffle [sic] their pockets for new vocabulary.
The word would be
aliterate. I fyou want to have word that uses only Latin affixes and roots, you could use the more common
illiterate. Another mixed one I mentioned earlier in this thread would be the semi-pseudo-mixed
unlettered. Or you could use the delightful (and totally Greek, man)
analphabetic.