mirth

Etymology

From Middle English merth, myrthe, murhthe, from Old English mergþ, mirgþ, myrgþ (“mirth, joy”), from Proto-West Germanic *murgiþu (“briefness, brevity”); equivalent to merry + -th. Cognate with Middle Dutch merchte (“pleasure, joy, delight”).

noun

1. The emotion usually following humour and accompanied by laughter
   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:
2. That which causes merriment.