Definition of birthday
1a : the day of a person's birthb : a day of origin
2 : an anniversary of a birth <her 21st birthday>
Examples of birthday in a sentence
Her birthday is September 30th.
Today is his 21st birthday.
The company just celebrated its 50th birthday.
First Known Use of birthday
BIRTHDAY Defined for English Language Learners
Definition of birthday for English Language Learners
: the day when someone was born or the anniversary of that day
: the day when something began
BIRTHDAY Defined for Kids
Definition of birthday for Students
1 : the day or anniversary of someone's birth
2 : a day of beginning <Our town just celebrated its 150th birthday.>
Seen and Heard
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