A.D.

or AD

1) use in the year of the Lord; since Christ was born: Charlemagne was born in a.d. 742

Etymology: L annō Dominī

2) gov assembly district

3) spo athletic director

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usage: The abbreviation a.d. was orig. placed before a date and is still usu. preferred in edited writing: The Roman conquest of Britain began in a.d. 43 (or, sometimes, began a.d. 43). The abbreviation b.c. (before Christ) is always placed after a date: Caesar was assassinated in 44 b.c. But by analogy with the position of b.c., a.d. is frequently found after the date in all types of writing: Claudius I lived from 10 b.c. to 54 a.d. This abbreviation may also designate centuries, being placed after the century specified: the second century a.d. Some writers prefer to use c.e. (Common Era) and b.c.e. (Before the Common Era) to avoid the religious overtones of a.d. and b.c.