Good man eyed new moon (8)
I believe the answer is:
ganymede
'moon' is the definition.
(I know that Ganymede is a moon of Jupiter)
'good man eyed new' is the wordplay.
'good' becomes 'g' (abbreviation).
'new' indicates anagramming the letters.
'man'+'eyed'='maneyed'
'maneyed' anagrammed gives 'anymede'.
'g'+'anymede'='GANYMEDE'
(Other definitions for ganymede that I've seen before include "beautiful boy" , "Trojan youth" , "Deny game, oddly, of the cupbearer to the gods" , "character 8 [OF SHAKESPEARE]" , "Beautiful cupbearer to the gods" .)