Largest moon in the solar system (8)
I believe the answer is:
ganymede
'largest moon in the solar system' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ganymede that I've seen before include "servant of God" , "Beautiful youth's" , "Cupbearer of Greek gods - largest moon of Jupiter" , "character 8 [OF SHAKESPEARE]" , "Beautiful youth" .)