Mirth is laughter and high spirits. Great mirth, a source of mirth, much mirth.
It is old-fashioned and slightly formal, and it names the shared kind rather than private amusement — mirth happens in a room. Mirthless, meaning without humour, is used far more than mirth itself now. Note merry, from which it comes with the old -th ending, as in warmth and strength.
1nounmirthLaughter and high spirits.
“His attempt to dance caused great mirth among his friends.”
mirth is amusement.
Old English myrgth is merry plus -th. Warmth and strength are formed with the same ending.
Proto-West Germanic
*murgīþu — briefness, brevity
Old English
myrgþ — mirth, joy
Middle English
merth
English, today
mirth
From Middle English merth, myrthe, murhthe, from Old English myrgþ (“mirth, joy”), from Proto-West Germanic murgīþu (“briefness, brevity”); equivalent to merry + -th. Cognate with Middle Dutch merchte (“pleasure, joy, delight”).
Etymology from Wiktionary, CC BY-SA