n.
A word, such as a preposition, a conjunction, or an article, that has little semantic content of its own and chiefly indicates a grammatical relationship. Also called form word, functor.
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.