"The use of the Coptic articles, both definite and indefinite, corresponds closely to the use of the articles in English....Indefinite nouns designating unspecified quantities of a substance require an indefinite article in Coptic where there is none in English....Abstract nouns, such as ME, truth, often appear with either article (OYME, TME} where English employs no article." -- Introduction to Sahidic Coptic, by Thomas O. Lambdin (Mercer University Press, 1983) p. 5
"HN TEHOYEITE NE.FSHOOP NGI PSHAJE
In the beginning -past tense marker- He exists -subject marker- the Word
AYW NEYNOUTE PE PSHAJE
And past tense marker - a-god is the Word." (John 1:1a, 1:1c)
-- Coptic in 20 Lessons, by Bentley Layton (Peeters Leuven, 2007) p. 7
Both Thomas Oden Lambdin and Bentley Layton are recognized Coptic scholars and grammarians. Layton actually diagrams John 1:1c on page 7 of his new book, released this year. I can't reproduce the Coptic fonts here, but you can see that he diagrams Coptic John 1:1c to say literally, "And was a god is the Word." Or in more smooth English, "And the Word was a god."
The Sahidic Coptic indefinite article, when before a common Coptic noun that is not abstract or representing a substance or a quality, is routinely rendered in English with the English indefinite article, "a." This can be verified by translations of the the Sahidic Coptic New Testament and other Sahidic Coptic literature.
If the context calls for it, OYNOUTE, "a god" literally, can be rendered into English adjectivally as "divine," according to Layton's grammar, page 34.
However, in the Coptic translation of John 1:1c, those are the only Coptic options: either "the Word was a god/divine being" or "the Word was divine." The Coptic indefinite construction cannot support the definite English translation: "the Word was God."
See also:
http://nwtandcoptic.blogspot.com