birthday

noun

birth·​day ˈbərth-ˌdā 

1

a

: the day of a person's birth

b

: 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.

Recent Examples on the Web

There are birthday announcements, and then there’s what Celine Dion just did. —Ryan Brennan, Kansas City Star, 31 Mar. 2026

Ericsson is celebrating its 150th birthday this year, while Experian’s roots stretch back nearly two centuries. —Francesca Cassidy, Fortune, 31 Mar. 2026

The Grammy-winner took to Instagram to share the news on Monday, which also marked her 58th birthday. —Jessica Schladebeck, New York Daily News, 31 Mar. 2026

In September 1879, the girl died of viral encephalitis — presumed to have been transmitted by a mosquito — just weeks before her 13th birthday. —Camila Pedrosa, Sacbee.com, 31 Mar. 2026

Word History

First Known Use

14th century, in the meaning defined at sense 2

Phrases Containing birthday

• birthday suit

Rhymes for birthday

• airway
• allay
• archway
• array
• ashtray
• astray
• aue
• away
• ballet
• belay
• beltway
• beret

Kids Definition

birthday

noun

birth·​day ˈbərth-ˌdā 

1

: the day or anniversary of one's birth

2

: the day or anniversary of a beginning