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-order1. 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)