Definition: A.D. is the Latin abbreviation for Anno Domini, which means 'in the year of our Lord,' or, more fully, anno domini nostri Jesu Christi 'the year of our Lord Jesus Christ.'
A.D. is used with dates in the current era, which is considered the era since the birth of Christ.
The counterpart to Anno Domini is B.C. for 'Before Christ.'
Because of A.D.'s obvious Christian overtones, many prefer to use more secular abbreviations like C.E. for 'Common Era.' However, many lay publications, like this one, still use A.D.
Although unlike English, Latin is not a word-order language, it is conventional in English writing for A.D. to precede the year (A.D. 2010) so that the translation, read in word order, would mean "in the year of our lord 2010". (In Latin, it wouldn't matter whether it was written A.D. 2010 or 2010 A.D.)
Note: The abbreviation a.d. may also stand for "ante diem" meaning the number of days before the kalends, nones, or ides of a Roman month. The date a.d.XIX.Kal.Feb. means 19 days before the kalends of February. Don't count on the a.d. for ante diem to be lower case. Inscriptions in Latin often appear only in capital letters.
Also Known As: Anno Domini
Alternate Spellings: AD (without the periods)
Examples: In A.D. 61 Boudicca led a rebellion against the Romans in Britain.
If the terms A.D. and B.C. confuse you, think of a number line with A.D. on the plus (+) side and B.C. on minus (-) side. Unlike the number line, there is no year zero.
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