adadvertisement, advertising: an ad agencyNot to be confused with:add ? to make an addition; to say or write further; to include: Be sure to add the tax.Abused, Confused, & Misused Words by Mary Embree Copyright © 2007, 2013 by Mary EmbreeADabbr.1. active duty2. air-dried3. or ad anno Domini4. A/D analog/digital5. athletic directorad 1 (?d)n. An advertisement.ad 2 (?d)n. An advantage in tennis.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.ad (æd) n short for advertisementad (æd) n (Tennis) short for advantage Brit equivalent: van ad the internet domain name for (Computer Science) Andorra AD abbreviation for 1. (indicating years numbered from the supposed year of the birth of Christ)anno Domini: 70 ad. Compare BC 2. (Military) military active duty 3. (Military) military air defence 4. Dame of the Order of Australia [(sense 4) Latin: in the year of the Lord] Usage: In strict usage, ad is only employed with specific years: he died in 1621 ad, but he died in the 17th century (and not the 17th century ad). Formerly the practice was to write ad preceding the date (ad 1621), and it is also strictly correct to omit in when ad is used, since this is already contained in the meaning of the Latin anno Domini (in the year of Our Lord), but this is no longer general practice. bc is used with both specific dates and indications of the period: Heraclitus was born about 540 bc; the battle took place in the 4th century bcCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ad1 (æd) n. 1. an advertisement. 2. advertising: an ad agency. [1835?45; by shortening] ad2 (æd) n. Tennis. advantage (def. 4). [1925?30; by shortening] ad- a prefix occurring in verbs or verbal derivatives borrowed from Latin, where it meant ?toward? and indicated direction, tendency, or addition: adjoin. For variants before a following consonant, see a-5, ac-, af-, ag-, al-, an-2, ap-1, ar-, as-, at-. [