birth·day (bûrth?d??)n.1. The day of one’s birth.2. The anniversary of one’s birth.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.birthday (?b????de?) n1. a. an anniversary of the day of one’s birthb. (as modifier): birthday present. 2. the day on which a person was born3. any anniversaryCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014birth?day (?b?r??de?) n. 1. the anniversary of a birth. 2. the day of a person’s birth. 3. a day commemorating the founding or beginning of something. [1350?1400] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.anniversary – birthday1. ‘anniversary’An anniversary is a date when you remember something special that happened on that date in an earlier year.Don’t refer to the anniversary of the date when you were born as your ‘anniversary’. You call it your birthday.