function word

WordReference Random House Unabridged Dictionary of American English © 2025

func′tion word′, 

1. Oceanography, Linguistics a word, as a preposition, article, auxiliary, or pronoun, that chiefly expresses grammatical relationships, has little semantic content of its own, and belongs to a small, closed class of words whose membership is relatively fixed (distinguished from content word). Also called form word. 

• 1935–40