Constellation — or moon of Jupiter given name? (5)
I believe the answer is:
orion
'constellation' is the definition.
(I know that Orion is a constellation)
'or moon of jupiter given name?' is the wordplay.
'moon of jupiter' becomes 'Io' (Io is a moon of Jupiter).
'given' is a charade indicator (letters next to each other).
'name?' becomes 'n' (common abbreviation e.g. on forms).
'or'+'io'+'n'='ORION'
(Other definitions for orion that I've seen before include "Major constellation" , "Mythical great hunter" , "Bright constellation, named after legendary Greek hunter" , "Constellation in the form of a belt" , "Heavenly figure" .)