One of the Marx Brothers takes on a barbed dart (7)
I believe the answer is:
harpoon
'a barbed dart' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'one of the marx brothers takes on' is the wordplay.
'one of the marx brothers' becomes 'harpo' (comedian Harpo Marx).
'takes' is a charade indicator (letters next to each other).
'harpo'+'on'='HARPOON'
Can you help me to learn more?
(Other definitions for harpoon that I've seen before include "Barbed whale-spear" , "Whaler's weapon" , "Whale spear" , "Whale-catching missile" , "Barbed whaling spear" .)