The Collaborative International Dictionary of English v.0.48:

Hessian \Hes"sian\, a.
   Of or relating to Hesse, in Germany, or to the Hessians.
   [1913 Webster]

   Hessian boots, or Hessians, boot of a kind worn in
      England, in the early part of the nineteenth century,
      tasseled in front. --Thackeray.

   Hessian cloth, or Hessians, a coarse hempen cloth for
      sacking.

   Hessian crucible. See under Crucible.

   Hessian fly (Zool.), a small dipterous fly or midge
      (Cecidomyia destructor). Its larv[ae] live between the
      base of the lower leaves and the stalk of wheat, and are
      very destructive to young wheat; -- so called from the
      erroneous idea that it was brought into America by the
      Hessian troops, during the Revolution.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hessian \Hes"sian\, n.
   1. A native or inhabitant of Hesse.
      [1913 Webster]

   2. A mercenary or venal person. [U. S.]
      [1913 Webster]

   Note: This use is a relic of the patriot hatred of the
         Hessian mercenaries who served with the British troops
         in the Revolutionary War.
         [1913 Webster]

   3. pl. See Hessian boots and cloth, under Hessian, a.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hessian
    n 1: (19th century) a man's high tasseled boot [syn: Hessian
         boot, hessian, jackboot, Wellington, Wellington
         boot]