Closed-class word

In linguistics, a closed class (or closed word class) is a word class to which no new items can normally be added, and that usually contains a relatively small number of items. Typical closed classes found in many languages are adpositions (prepositions and postpositions), determiners, conjunctions, and pronouns.
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Noun
1. a word that is uninflected and serves a grammatical function but has little identifiable meaning
(synonym) function word
(hypernym) word
(hyponym) determiner, determinative
(part-meronym) grammatical meaning