ad 1 (?d)n. An advertisement.ad 2 (?d)n. An advantage in tennis.ADabbr.1. active duty2. air-dried3. or ad anno Domini4. A/D analog/digital5. athletic directorAmerican 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.a/d abbreviation for after date Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014