“Church key?” he queried, and when he tapped the bottle top she realized he meant an opener. (Alexandra Sokoloff, in The Unseen)
Although Wikipedia has a piece on the origins of the term, ‘church key’, I enjoyed reading the derivation given by World Wide Words. An organisation calling itself Just for Openers has some good pictures.
Sokoloff, Alexandra. 2009. The unseen. New York: St Martin’s Press [p108]