Scheme is extremely efficient for getting heavenly body (6)
I believe the answer is:
planet
'heavenly body' is the definition.
(planet is a type of heavenly body)
'scheme is extremely efficient' is the wordplay.
'scheme' becomes 'plan' (synonyms).
'is extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'efficient' with its middle taken out is 'et'.
'plan'+'et'='PLANET'
'for getting' acts as a link.
(Other definitions for planet that I've seen before include "Orbiting body in the heavens" , "Celestial body orbiting round a star" , "Mars or Uranus" , "Sun's orbiter" , "Celestial body orbiting around a star" .)