birthday

Etymology

From Middle English birthdai, birtheday, from Old English ġebyrddæġ (“birthday”), influenced by Old Norse burðr, equivalent to birth + day. Compare Saterland Frisian Gebuursdai (“birthday”), Dutch geboortedag (“birthday”), Low German Geboortsdag (“birthday”), German Geburtstag (“birthday”), Norwegian bursdag, gebursdag (“birthday”). Eclipsed non-native Middle English nativitee (“birth, nativity, birthday”), from Old French nativité, nativited, from Latin nātīvitas.

noun

1. The anniversary of the day on which someone is born.
   When's your birthday? Mine's on April 1.
   1903, L. Frank Baum, The Surprising Adventures of the Magical Monarch of Mo and His People, The Fifth Surprise: The Monarch Celebrates His Birthday, One of the Wise Men said the King was born in February; another declared it was in May, and a third figured the great event happened in October. So the King issued a royal decree that he should have three birthdays every year, in order to be on the safe side; and whenever he happened to think of it he put in an odd birthday or two for luck.
   1906, Edith Nesbit, The Railway Children, Chapter 9: The pride of Perks, "And we thought we'd make a nice birthday for him. He's been so awfully jolly decent to us, you know, Mother," said Peter, "and we agreed that next bun-day we'd ask you if we could."
   c. 1911, Cotton Mather, Worthington Chauncey Ford (editor), Diary of Cotton Mather, Volume 1: 1681-1708, footnote, page 1, It was his custom to begin a new year's record on February 12, his birthday.
   The King's Birthday, which occurred yesterday, will be officially observed to-day, and the customary list of honours conferred on the occasion is published. June 4 1921, “Birthday Honours — Companions of Honour”, in The Times
2. The anniversary of the day on which something is created.
3. The date on which someone is born or something is created, more commonly called birthdate or date of birth.
4. A birthday party.
   I'd like to invite you all to my birthday.

verb

1. (intransitive, informal) To celebrate one's birthday.