This paper focuses on the morpheme bɔ̀ in the Cameroonian Bantu language Eton (A71), which should be identified as the nominal prefix of class 2a according to the traditional criteria and terminology. It will be shown that this morpheme is not a prefix but a word, probably a proclitic. Its function is to pluralize a following genderless word. Since the most typical genderless words are proper names and deictically restricted kinship terms (e.g. tàdá 'my father'), the result is usually an associative plural. This explains how the succession of the locative preposition á and the plural word could grammaticalise into the complex preposition ábɔ̂ 'chez'. The behaviour of bɔ̀ in Eton confirms some observations that Matthew Dryer (1989) made in his typological study on plural words. The end of this paper presents a brief comparative overview of the class 2a marker in other Bantu languages.