God poisoned by mistake (8)
I believe the answer is:
poseidon
'god' is the definition.
(Poseidon is an example)
'poisoned by mistake' is the wordplay.
'by mistake' indicates anagramming the letters.
'poisoned' anagrammed gives 'POSEIDON'.
(Other definitions for poseidon that I've seen before include "being able to create waves?" , "Poisoned the Greek god of the sea" , "I snooped to find Greek god of the sea" , "Greek sea-god" , "Greek god of the sea and earthquakes" .)