The term is a traditional term used for words which (a) end in a plural affix, (b) have a plural meaning, and (c) do not have a singular counterpart.
The plural of plurale tantum is pluralia tantum (see section "Origin").
Examples of English pluralia tantum are trousers, scissors, scales.
In Dutch plural nouns can be formed by adding the suffix -en (hond-honden 'dog(s)'). But some nouns such as hersenen 'brains', annalen 'annals' and watten 'cotton wadding' have a plural meaning, end in the plural affix -en, and have no singular counterpart (*hersen, *annaal, *wat).
Tantum is from Latin and means 'only', and plurale is the Latin form of plural. So plurale tantum is originally a Latin phrase meaning 'plural only'. The Latin plural of plurale is pluralia.
- Scalise, S. 1984. Generative Morphology, Foris, Dordrecht.
- Vraciu, Ariton. 1976. Considérations sur l'emploi des noms pluralia tantum dans les langues baltiques, slaves et finno-ougriennes. Acta Baltico-Slavica 9: 27-37. (Wrocław)