Lewis Short
hĭlărĭtūdo (noun F) : hilaris
* Cheerfulness, merriment (ante-class. for the class. hilaritas): numquam ego te tristiorem Vidi esse: quid cedo tam abhorret hilaritudo? Plaut. Cist. 1, 1, 56: onera te hilaritudine,id. Mil. 3, 1, 83: ut in ocellis hilaritudo est!id. Rud. 2, 4, 8.
Charlton T. Lewis, Charles Short, A Latin Dictionary