To laugh uproariously. This hyperbole dates from the seventeenth century. Thomas Brown used it in Saints in Uproar (1687): “You’d break a man’s sides with laughing.” The word “split” came into use somewhat later. Dickens used it in The Old Curiosity Shop (1840), “He bade fair to split his sides with laughing,” and Harriet Beecher Stowe in Uncle Tom’s Cabin (1852), “I laughed fit to split.” See also shake with laughter.