\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.