/ Thesaurus / F Synonyms of firth of forth Find synonyms for: Noun1. Firth of Forthusage: a large firth on the east coast of Scotland and the estuary of the Forth River; location of EdinburghWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: dormant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language