Ou: The Coptic Letter (Value 70), from Greek Omicron

Ou is the sixteenth letter of the Coptic alphabet and carries the numeral value seventy. It is the Greek omicron, whose Greek name means small o and was invented by grammarians to keep it apart from the long omega; Coptic did not adopt that name, and its grammars record the letter as ou. It writes a short o, and it forms half of a pair with omega that lets Coptic mark a vowel distinction no earlier Egyptian script could show. That pair is one of the workhorses of Coptic dialectology. The dialects divide the space between the two letters differently, so a word written with ou in Sahidic may appear with omega in Bohairic or in one of the smaller regional forms, and tables of those correspondences are among the first tools an editor reaches for when a manuscript has to be placed. Ou also takes part in a spelling that surprises beginners.

Coptic has no single letter for the u vowel and writes it, as Greek does, with the sequence ou, so the letter appears constantly in a role that has nothing to do with its own value as a short o. The pairing with omega has a further consequence for anyone reading Coptic in translation or in a modern edition. Editors normalise, and a printed Sahidic text will often present a spelling drawn from the dominant manuscripts of that dialect rather than from the particular witness in front of them, with the variants pushed into an apparatus at the foot of the page. Those variants are frequently a matter of ou against omega and nothing else, so a reader who ignores the apparatus is ignoring most of what the manuscripts actually disagree about. Ou is also worth watching because it is the first element of the digraph that writes the u vowel, which means a large share of its appearances on a page are not the letter doing its own work at all.