Greek god is poisoned, unfortunately (8)
I believe the answer is:
poseidon
'greek god' is the definition.
(Poseidon is an example)
'poisoned unfortunately' is the wordplay.
'unfortunately' is an anagram indicator.
'poisoned' anagrammed gives 'POSEIDON'.
'is' is the link.
(Other definitions for poseidon that I've seen before include "associated with adventure on screen" , "Olympian" , "Greek sea-god" , "underwater missile" , "Poisoned the Greek god of the sea" .)