/ Thesaurus / U Synonyms of u boat Find synonyms for: Noun1. submarine, pigboat, sub, U-boat, submersible, submersible warshipusage: a submersible warship usually armed with torpedoesWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: inutiae Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language