The unleavened bread that Jews eat at Passover is called the azyme; in contrast, the leavened bread that members of the Greek Orthodox Church eat at communion is called the enzyme. The final syllable that these two words share derives from a Greek word meaning leaven, leaven being an ancient agent of fermentation. The two words differ only in their prefixes: the a of azyme is a Greek prefix that means not, whereas the en of enzyme is a Greek prefix that means in. Of these two words, azyme is the oldest, appearing briefly in English in the fourteenth century, and then vanishing until the sixteenth century: during those intervening years England had banished all Jews from its shores. The other word, enzyme, did not appear in English until the mid nineteenth century; forty years later, near the end of the nineteenth century, biochemists gave new life to this somewhat obscure religious term when they gave the name enzyme to proteins that cause biochemical reactions similar to those produced by leavening agents.