Webster's Dictionary's definition of "affair" (1830).
Noah Webster, "Affair" in An American Dictionary of the English Language, 4th ed. (New York: S. Converse, 1830), 17
AFFAIR, n. [Fr. affare.] 1. Business of any kind; that which is done, or is to be done. In the plural, it denotes transactions in general; as human affairs. 2. Matters; state; condition of business or concern. 3. In the singular, it is used for a private dispute, or duel; as, an affair of honor; and sometimes a partial engagement of troops.