The Collaborative International Dictionary of English v.0.48:

Orbital \Or"bit*al\, a.
   Of or pertaining to an orbit. "Orbital revolution." --J. D.
   Forbes.
   [1913 Webster]

   Orbital index (Anat.), in the skull, the ratio of the
      vertical height to the transverse width of the orbit,
      which is taken as the standard, equal to 100.
      [1913 Webster]