Whaling spear (7)
I believe the answer is:
harpoon
'whaling spear' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for harpoon that I've seen before include "Whale spear" , "Type of spear" , "killer at sea" , "Spear with a line attached for fishing" , "Anti-whale weapon" .)