/ Thesaurus / U Synonyms of upper carboniferous period Find synonyms for: Noun1. Pennsylvanian, Pennsylvanian period, Upper Carboniferous, Upper Carboniferous periodusage: from 310 million to 280 million years ago; warm climate; swampy landWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: acquiesce Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language