plurale tantum
/plʊəˌreɪli ˈtant(ə)m/Grammar
noun
A noun which is used only in plural form, or which is used only in plural form in a particular sense or senses.
Origin
Late 19th century; earliest use found in American Journal of Philology. From classical Latin plūrāle the plural, use as noun of neuter of plūrālis + tantum only.