The Collaborative International Dictionary of English v.0.48:
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.
[1913 Webster]
By God and by this porthors I you swear. --Chaucer.
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The Collaborative International Dictionary of English v.0.48:
Portos \Por"tos\, n.
See Portass. [Obs.]
[1913 Webster]