(By Hannah J. Haynie): "A noun class/gender system categorizes nouns for the purposes of grammatical agreement with other constituents in the noun phrase or other inflectional morphology. See the classification wiki page for more information on our definition of noun class/gender. Noun class/gender assignment may be based on one or several factors. This feature asks whether the noun class/gender system of a language includes a large or open class of nouns whose assignment to that class is not predictable based on phonology or semantics. In other words, such a class will appear to be assigned arbitrarily. ❡
Keep in mind that it is common for noun classes to include members that are not entirely predictable. Noun classes that are generally organized around a semantic or phonological property may also include some idiosyncratic members. The arbitrary assignment of some nouns to otherwise semantically or phonologically defined classes is not what this feature targets."