/ Thesaurus / 1 Synonyms of 1st class Find synonyms for: Noun1. first class, 1st class, first-class mail, 1st-class mail, mailusage: mail that includes letters and postcards and packages sealed against inspectionWordNet 3.0 Copyright © 2006 by Princeton University. All rights reserved. Related Content Daily Word Quiz: loathe Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language