Adjective
orthochronous (not comparable)
(mathematics) Describing any Lorentz transformation or Galilean transformation which preserves the direction of time
The orthochronous, proper, proper orthochronous sets of LTs are all subgroups. Source: Internet
This will not always be the case; it can be shown that the composition of any two Lorentz transformations always has the positive determinant and positive inequality, a proper orthochronous transformation. Source: Internet