Definition of "birthday"

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

1838, Boz [pseudonym; Charles Dickens], chapter 2, in Oliver Twist; or, The Parish Boy’s Progress. […], volumes (please specify |volume=I, II, or III), London: Richard Bentley, […]

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.

1903, L. Frank Baum, The Surprising Adventures of the Magical Monarch of Mo and His People, The Fifth Surprise: The Monarch Celebrates His Birthday

"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."

1906, Edith Nesbit, The Railway Children, Chapter 9: The pride of Perks

It was his custom to begin a new year's record on February 12, his birthday.

c. 1911, Cotton Mather, Worthington Chauncey Ford (editor), Diary of Cotton Mather, Volume 1: 1681-1708, footnote, page 1

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.

1921 June 4, “Birthday Honours — Companions of Honour”, in The Times