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.
© Webster 1913.