Overseas game bird (6)
I believe the answer is:
osprey
'bird' is the definition.
(osprey is a kind of bird)
'overseas game' is the wordplay.
'overseas' becomes 'os' (I am not sure about this - if you are sure you should believe this answer much more).
'game' becomes 'prey' (both can mean animals which are hunted).
'os'+'prey'='OSPREY'
Can you help me to learn more?
(Other definitions for osprey that I've seen before include "Fish-hawk" , "Fish eagle" , "Large fish-eating bird of prey" , "Large bird that preys on fish in inland waters" , "Spy roe (anag)" .)