The entire family is characterised by a paucity of phonemic vowels (two or three, depending upon the analysis) coupled with rich consonantal systems that include many forms of secondary articulation. Ubykh (Ubyx), for example, had both the minimal number of vowels (two), and probably the largest inventory of consonants outside Southern Africa.
Linguistic reconstructions suggest that both the richness of the consonantal systems and the poverty of the vocalic systems may be the result of a historical process, whereby vowel features such as labialisation and palatalisation were reassigned to adjacent consonants. For example, ancestral */ki/ may have become /kʲə/ and */ku/ may have become /kʷə/, losing the old vowels */i/ and */u/ but gaining the new consonants /kʲ/ and /kʷ/. The linguist John Colarusso has further postulated that some instances of this may also be due to the levelling of an old grammatical class prefix system (so */w-ka/ may have become /kʷa/), on the basis of pairs like Ubykh /ɡʲə/ vs. Kabardian and Abkhaz /ɡʷə/ heart. This same process is claimed by some to lie behind the development of labiovelars in Proto-Indo-European which once neighboured Proto-NWC.
Northwest Caucasian languages have rather simple noun systems, with only a handful of cases at the most, coupled with highly agglutinative verbal systems that can contain almost the entire syntactic structure of the sentence. All finite verbs are marked for agreement with three arguments: absolutive, ergative, and indirect object, and there are also a wide range of applicative constructions. There is a split between "dynamic" and "stative" verbs, with dynamic verbs having an especially complex morphology. A verb's morphemes indicate the subject's and object's person, place, time, manner of action, negative, and other types of grammatical categories.
Northwest Caucasian languages do not generally permit more than one finite verb in a sentence, which precludes the existence of subordinate clauses in the Indo-European sense. Equivalent functions are performed by extensive arrays of nominal and participial non-finite verb forms, though Abkhaz appears to be developing limited subordinate clauses, perhaps under the influence of Russian.
Circassian (Cherkess) is a cover term for the series of dialects that include the literary languages of Adyghe and Kabardian.