§8. Noun Structure. With the exception of those of Class 10, nouns in Chichewa are composed of two formatives: stem and prefix, generally speaking, but in numerous cases only the stem is represented. However, in a number of instances the nouns which are used without prefixes in the singular require prefixation in the plural. For some, nouns of Class 5, e. g., it can be said definitely that the prefixes have disappeared or are ‘worn down’, since they can be easily recognized in cognate words of other Bantu languages. 1 It requires more historical perspective to make a similar statement for many other nouns.
A 1937 study studied this question.