Choir - quire

The two forms choir and quire are, mostlyt, different spellings of the same word.

OED: "Etymology: Middle English quer, quere, < Old French cuer choir of a church (modern French chœur) < Latin chorus company of dancers, dance; company, band; (in medieval Latin) body of singers in church, place for singers in church; < Greek χορός dance, company of dancers or singers: compare chorus n. The change from Middle English quēre, to quyer, quire, goes exactly with that of brere and frere to brier, friar. The spoken word is still quire, though since the close of the 17th cent. this has been ficctitiously spelt choir, apparently as a partial assimilation to Greek-Latin chorus, or French chœur.

The spelling quire has never been altered in the English Prayer-book. Some people affect to pronounce choir /kɔɪə(r)/ .