Portass \Por"tass\, n. [OF. porte-hors a kind of prayer book, so called from being portable; cf. LL. portiforium.] A breviary; a prayer book. [Written variously {portace}, {portasse}, {portesse}, {portise}, {porthose}, {portos}, {portus}, {portuse}, etc.] [Obs.] --Spenser. Camden. By God and by this porthors I you swear. --Chaucer.