Choir - quire

The two forms choir and quire are, mostly, different spellings of the same word. Choir is the usual spelling in current English, although quire is the better representation of the pronunciation of the word in either spelling - IPA: /kwaɪə^r/.

OED gives the etymology as from the Middle English quer, or quere, which became quyer or quire in a regular change, which can be paralleled in the history of (modern) 'friar' and 'briar'. It adds: "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 chœur." (Sincre thisdisd the ultimate derivation, OED's 'fictitious' is hard to understand.) The ultimate origin is the Greek χορός (chorus) 'dance', 'company of dancers or singers', through the medieval Latin meaning of 'body of singers in church', 'place for singers in church'. This became cuer in Old French ('choir of a church') and chœur in modern French.

"The spelling quire has never been altered in the English Prayer-book. Some people affect to pronounce choir /kɔɪə(r)/ 'koh-ih-err']" (OED).