birthday

noun

1. The anniversary of the day on which someone is born.

   “When's your birthday? Mine's on April 1.”

   “I'll be thirty-seven (years old) next birthday.”

   “Oliver Twist's ninth birthday found him a pale thin child, somewhat diminutive in stature, and decidedly small in circumference.”

   “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."”

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