/ Thesaurus / T Synonyms of thumb index Find synonyms for: Noun1. thumb index, notchusage: one of a series of rounded notches in the fore edge of a book to indicate sectionsWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: ravenous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language