c. 1200, "set of four folded pages for a book; pamphlet consisting of a single quire," from Anglo-French quier, Old French quaier "sheet of paper folded in four," from Vulgar Latin *quaternus, from Latin quaterni "four each," from quater "four times." Meaning "standard unit for selling paper" first recorded late 14c. In quires (late 15c.) means "unbound."
quire (n.2)
early form and later variant spelling of choir (q.v.).