The Collaborative International Dictionary of English v.0.48:

Preorder \Pre*or"der\, v. t.
   To order to arrange beforehand; to foreordain. --Sir W.
   Hamilton.
   [1913 Webster]

The Free On-line Dictionary of Computing (30 December 2018):

pre-order

   

   1. traversal.

   2. A relation R is a pre-order if it is reflexive
   (x R x) and transitive (x R y R z => x R z).  If it is also
   antisymmetric (x R y R x => x = y) then it is a partial
   ordering.

   (2001-10-01)