Webster's Revised Unabridged Dictionary · 1913

Jess

Jess , noun

[Old French gies, giez, prop. plural of giet, get, jet, French jet, a throwing, jess. See Jet a shooting forth.]

A short strap of leather or silk secured round the leg of a hawk, to which the leash or line, wrapped round the falconer's hand, was attached when used. See Illust. of Falcon.
Like a hawk, which feeling freed From bells and jesses which did let her flight. — Spenser