SLACK. 1. A-Sax. slaec, slack, remiss, idle, lazy. A Norfolk correspondent says : " I knew a man whose real name was Harris, who, from his extreme laziness, always went by the name of Slack." 2. A topographical word thus variously defined by Jamicson : "i. An opening in the higher part of a hill or mountain, where it becomes less steep, and forms a sort of pass. ii. A gap or narrow pass between two hills or mountains, iii. A morass."

Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.