/ Dictionary / Index F fill-in: Meaning and Definition of Find definitions for: fill-in Pronunciation: (fil'in"), [key] — n. a person or thing that fills in, as a substitute, replacement, or insertion: The company used a fill-in for workers on vacation. a brief, informative summary; a rundown. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: fill-in (Thesaurus) fillet weld filling Related Content Daily Word Quiz: pristine Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language