function word

noun1

1. •
   A word that has little meaning when standing alone, but instead serves to express grammatical relationships with other words within a sentence, or specify the attitude or mood of the speaker, including conjunctions, prepositions, pronouns, auxiliary verbs, certain frequent adverbs.

   • Durrant (2009), for example, developed a list of 1000 academic two-word bigrams, of which 763 were lexical words combined with function words. — 2018