A little follow-up on the previous post, based mainly on Reintges' Coptic Egyptian (Sahidic Dialect): A Learner's Grammar:
In Coptic, predication of properties is handled exactly as for nouns, including the use of an determiner with the adjective:
hen-noc gar ne neu-polytia
indef.pl-great for are their-labours.
For their labours are great.
In attribution, the structure is Determiner - A - n - B, where A can be the noun and B the adjective, or vice versa:
ou-kohi n-soouhs: a-small n convent
t-parthenos n-sabê: the-virgin n prudent
To express the material of which something is made, you use the same structure, except that only B can be the material:
t-kloole n-ouein: the-cloud n light "the cloud of light"
Note that this is separate from the attributive construction:
ntof pe-iôt pahôm "He, our father Pahom"
So can adjectives be distinguished as a separate word class, when they behave so much like nouns? The answer is yes: an adjective is an item that can occupy either A or B in the attributive structure without a change in referential meaning. (See Coptic Grammatical Categories, Shisha-Halevy, p. 53.) If you reverse the constituents of a genitive or material construction, you change the referential meaning: "a vessel of wood" vs. "vessel wood (ie wood for vessels.)" If you do so for an adjective-noun attributive construction, the referential meaning stays the same: ou-noc n-polis or ou-polis n-noc both refer to the same entity, "a big city". So for this case, Dixon's hypothesis scrapes through.