Neptune, say (6)
I believe the answer is:
planet
'neptune say' is the definition.
(Neptune is an example)
This is all the clue.
(Other definitions for planet that I've seen before include "Celestial body orbiting around a star" , "Eg, Mars or Pluto" , "One orbiting star" , "Mars or Uranus" , "Celestial body orbiting round a star" .)