Source : Webster's Revised Unabridged Dictionary (1913)

Anno Domini \An"no Dom"i*ni\ [L., in the year of [our] Lord
   [Jesus Christ]; usually abbrev. a. d.]
   In the year of the Christian era; as, a. d. 1887.

Source : WordNet®

anno Domini
     adv : in the Christian era; used before dates after the supposed
           year Christ was born; "in AD 200" [syn: {AD}, {A.D.}]