c. 1300, "thong for holding a dog or hound," from Old French lesse, laisse "hound's leash," ultimately from Latin laxus "loose" (see lax), perhaps via noun use of fem. form laxa. The notion seems to be of a string loosely held. Figurative sense attested from early 15c. The meaning "a set of three, three creatures of a kind" is from early 14c., originally in sporting language and especially of greyhounds, foxes, bucks, or hares.
"to attach to or with a leash," 1590s, from leash (n.). Related: Leashed; leashing.