Patch of land I almost killed off (4)
I believe the answer is:
isle
'patch of land' is the definition.
'isle' can be an answer for 'land' (isle is a kind of land). I'm not sure about the 'patch of' bit.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for isle that I've seen before include "Dogs, say" , "Sea-girt area" , "Wight, Man or Skye" , "Skye, for instance" , "This could be key" .)