Ksi and the Awkward Fit of a Borrowed Alphabet

No alphabet transfers cleanly from one language to another. The Greek alphabet came to Egyptian with letters for sounds Egyptian did not have, with cluster letters Egyptian did not need, with a numeral series requiring three signs that write nothing at all, and without letters for a whole set of Egyptian sounds. Coptic handled each of these differently. The unneeded letters were kept and used for loanwords and numerals. The cluster letters became optional shorthands, which is why ksi is uncommon. The numeral signs were kept as figures only. And the missing sounds were supplied by borrowing seven letters from Demotic, the cursive Egyptian script the new system was replacing. That last decision is the one that makes Coptic more than transliterated Egyptian.

Writing a language in a foreign alphabet without adaptation produces something a native speaker can barely use, and the history of missionary orthographies is full of examples. The people who settled the Coptic system did not do that. They kept the Greek series whole, then extended it, and the resulting alphabet served Egyptian for the entire span of its remaining written life and continues to serve the liturgy of the Coptic Orthodox Church today. Ksi, a letter half the alphabet could do without, is part of the same settlement.