/ Thesaurus / 1 Synonyms of 18th Find synonyms for: Adjective1. eighteenth, 18th, ordinal (vs. cardinal)usage: coming next after the seventeenth in positionWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: kiln Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language