mem·bra·nous \ˈmembrənəs, (ˈ)mem|brān-\adjective Etymology: Middle French membraneux, from membran- + -eux -ous 1.: of, relating to, or resembling membrane < a membranous lining > 2.: thin, pliable, and often somewhat transparent < membranous leaves > 3.: characterized or accompanied by the formation of a membrane or pseudomembrane < membranous croup > < membranous gastritis > • mem·bra·nous·lyadverb