Anno Domini

Various authorities support the different styles:

• anno domini
• anno Domini

From the Latin annō Domini (“in the year of the Lord”) from the word annō (“in the year”) the ablative of annus (“year”) + Domini (“of the Lord”) the genitive of Dominus (“the Lord”).

Anno Domini (not comparable)

1. In the year of our Lord (often abbreviated A.D. or AD).
   • 1620 — Mayflower Compact

     In Witness whereof we have hereunto subscribed our names at Cape Cod the eleventh of November, in the Reign of our Sovereign Lord, King James of England, France and Ireland, the eighteenth, and of Scotland the fifty-fourth. Anno Domini, 1620.

   • 1859 — Charles Dickens, A Tale of Two Cities

     The scene was Mr. Cruncher’s private lodging in Hanging-sword-alley, Whitefriars: the time, half-past seven of the clock on a windy March morning, Anno Domini seventeen hundred and eighty.

• See AD.

• (in the year of our Lord): a.d., AD, A.D., CE, Common Era, in the year of our Lord

• (in the year of our Lord): BC, B.C., BCE

• Anno Hegirae
• Wikipedia discussion of style