A.D. Look up A.D. at Dictionary.com
1570s, from Latin Anno Domini "Year of the Lord." Put forth by Dionysius Exiguus in 527 or 533 C.E., but used at first only for Church business. Introduced in Italy in 7c., France (partially) in 8c. In England, first found in a charter of 680 C.E. Ordained for all ecclesiastical documents in England by the Council of Chelsea, July 27, 816.

The resistance to it in part might have come because Dionysius chose 754 A.U.C. as the birth year of Jesus, while many early Christians would have thought it was 750 A.U.C. [See John J. Bond, "Handy-Book of Rules and Tables for Verifying Dates With the Christian Era," 4th ed., London: George Bell & Sons, 1889] A.C., for Anno Christi, also was common 17c.