The Collaborative International Dictionary of English v.0.48:

Heriot \Her"i*ot\, n. [AS. heregeatu military equipment, heriot;
   here army + geatwe, pl., arms, equipments.] (Eng. Law)
   Formerly, a payment or tribute of arms or military
   accouterments, or the best beast, or chattel, due to the lord
   on the death of a tenant; in modern use, a customary tribute
   of goods or chattels to the lord of the fee, paid on the
   decease of a tenant. --Blackstone. Bouvier.
   [1913 Webster]

   Heriot custom, a heriot depending on usage.

   Heriot service (Law), a heriot due by reservation in a
      grant or lease of lands. --Spelman. Blackstone.
      [1913 Webster]