Marx Brother talking about whale-killer (7)

I believe the answer is:
harpoon
'whale-killer' is the definition.
I can't judge whether this defines the answer.
'marx brother talking about' is the wordplay.
'marx brother' becomes 'harpo' (I've seen this in another clue).
'talking about' becomes 'on' (on can mean relating to or about a certain subject).
'harpo'+'on'='HARPOON'
Can you help me to learn more?
(Other definitions for harpoon that I've seen before include "Whaler's weapon" , "Barbed whaling spear" , "Type of spear" , "Whale-catching missile" , "Whaling weapon" .)
