Policeman seen with Shaft can be a venomous beast (8)
I believe the answer is:
stingray
'a venomous beast' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'policeman seen with shaft' is the wordplay.
'policeman' becomes 'sting' (I am not sure about this - if you are sure you should believe this answer much more).
'seen with' says to put letters next to each other.
'shaft' becomes 'ray' (synonyms).
'sting'+'ray'='STINGRAY'
'can be' acts as a link.
Can you help me to learn more?
(Other definitions for stingray that I've seen before include "Marine creature with venomous tail" , "swimmer" , "Poisonous spined fish" , "Dangerous fish" , "Flatfish with barbed spine" .)