Eta: The Coptic Letter (Value 8), from Greek Eta

Eta is the eighth letter of the Coptic alphabet and carries the numeral value eight. In classical Greek it wrote a long e, held distinct from the short e of epsilon, and Coptic maintained a genuine distinction between the two vowels. That distinction is one of the great gains the Greek alphabet brought to Egyptian. The older Egyptian scripts wrote consonants and left vowels unrecorded, so a word could not show on the page whether its vowel was long or short, front or back; Coptic can, and does, with the result that the vowel systems of the Coptic dialects can be described in a way that the vowel system of Middle Egyptian cannot. Eta carries part of that load.

The letter also demonstrates that the sound of a script and the sound of a liturgy can part company over time. Greek eta shifted towards an i sound during the Byzantine period, and the Bohairic reading used in the services of the Coptic Orthodox Church followed the same path, so the letter is now pronounced in church as a long i even though the spellings it appears in were fixed when it was a long e. Neither reading is a corruption of the other; they are two points on a line, and the manuscripts record the earlier one while the living tradition carries the later.