pluralizer
/ˈplʊərəlʌɪzə/ /ˈplʊər(ə)lʌɪzə/ /ˈplɔːrəlʌɪzə/noun
1A thing which renders something plural. rare.
2 Grammar. A suffix, prefix, inflection, or auxiliary word which forms a plural.
Origin
Mid 19th century; earliest use found in Putnam's Monthly Magazine. In sense 1 from pluralize + -er.