Ei: The Coptic Letter (Value 5), from Greek Epsilon

Ei is the fifth letter of the Coptic alphabet, worth five in the numeral series, and it is the Greek epsilon under a different name. The Greek label epsilon means bare or plain e, a term Greek grammarians coined late in order to distinguish the letter from a competing two letter spelling of the same sound; Coptic never adopted that label and its own tradition calls the letter ei.

The letter writes a short e. What makes it important out of proportion to its plainness is the amount of grammatical work Coptic gives it. Coptic builds a great deal of its grammar out of short prefixed elements, and ei appears in a large number of them, in the definite and indefinite articles, in verbal prefixes, and as the vowel that breaks up consonant clusters an Egyptian speaker would otherwise have to negotiate unaided. Reading a line of Coptic aloud is possible in a way that reading a line of Demotic is not, and letters like ei are the reason. Egyptian had been written for three millennia in scripts that recorded consonants only, and the switch to the Greek alphabet made the vowels of the language visible for the first time. Coptic is therefore the single stage of Egyptian whose pronunciation can be read rather than reconstructed, and everything scholars think they know about the vocalisation of earlier Egyptian leans on it.