The Collaborative International Dictionary
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.]
By God and by this porthors I you swear.
n. (obsolete form of portass English)