Definition of "mirth"

And he began to laugh again, and that so heartily, that, though I did not see the joke as he did, I was again obliged to join him in his mirth.

1881–1882, Robert Louis Stevenson, Treasure Island, London, Paris: Cassell & Company, published 14 November 1883

She was a fat, round little woman, richly apparelled in velvet and lace, […]; and the way she laughed, cackling like a hen, the way she talked to the waiters and the maid, […]—all these unexpected phenomena impelled one to hysterical mirth, and made one class her with such immortally ludicrous types as Ally Sloper, the Widow Twankey, or Miss Moucher.

1918, W. B. Maxwell, chapter 2, in The Mirror and the Lamp‎

Their eyes met and they began to laugh. They laughed as children do when they cannot contain themselves, and can not explain the cause of their mirth to grown people, but share it perfectly together.

1912, Willa Cather, The Bohemian Girl:

Phantasmal mirth, folded away: muskperfumed.

1922 February, James Joyce, Ulysses, Paris: Shakespeare and Company, […]