/ Thesaurus / L Synonyms of lengthiness Find synonyms for: Noun1. extension, lengthiness, prolongation, longnessusage: amount or degree or range to which something extends; "the wire has an extension of 50 feet"2. lengthiness, prolongation, continuation, protraction, duration, lengthusage: the consequence of being lengthened in durationWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: tenacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language