Source : Webster's Revised Unabridged Dictionary (1913)

Jess \Jess\, n.; pl. {Jesses}. [OF. gies, giez, prop. pl. of
   giet, get, jet, F. jet, a throwing, jess. See {Jet} a
   shooting forth.] (falconry)
   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.