In part, track orbiter (6)
I believe the answer is:
planet
'orbiter' is the definition.
(I've seen this before)
'in part track' is the wordplay.
'in' is an insertion indicator.
'part' becomes 'pt' (I've seen this in other clues**).
'track' becomes 'lane'.
'pt' enclosing 'lane' is 'PLANET'.
(Other definitions for planet that I've seen before include "Mars or Uranus" , "massive revolver" , "Celestial body orbiting around a star" , "Jupiter is one" , "Large body orbiting sun" .)