Pointed instrument with a piece of rope on (7)
I believe the answer is:
harpoon
'pointed instrument' is the definition.
'harpoon' can be an answer for 'instrument' (thesaurus). I am unsure of the 'pointed' bit.
'with a piece of rope on' is the wordplay.
'with' means one lot of letters go next to another.
'a piece of rope' becomes 'harpo' (I am not sure about this - if you are sure you should believe this answer much more).
'harpo'+'on' is 'HARPOON'.
Can you help me to learn more?
(Other definitions for harpoon that I've seen before include "Weapon for whales" , "Whaling weapon" , "Spear for old whaler" , "Whale spear" , "One's cast out at sea" .)