Choir - quire
The two forms choir and quire are, mostly, different spellings of the same word. Choir is the usual spelling in current Englsi, although quire is the better representation of the pronunciation of the word in either spelling - IPA: /kwaɪər/.
OED: "Etymology: Middle English quer, quere, < Old French cuer choir of a church (modern French chÅ“ur) < Latin chorus company of dancers, dance; company, band; (in medieval Latin) body of singers in church, place for singers in church; < Greek χοÏός dance, company of dancers or singers: compare chorus n. The change from Middle English quÄ“re, 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 fictitiously spelt choir, apparently as a partial assimilation to Greek-Latin chorus, or French chÅ“ur.
The spelling quire has never been altered in the English Prayer-book. Some people affect to pronounce choir /kɔɪə(r)/ .