Plan in principle getting cut down (4)
I believe the answer is:
idea
'plan' is the definition.
(both can mean an intention)
'principle getting cut down' is the wordplay.
'principle' becomes 'ideal' (I've seen this before).
'getting cut down' means to remove the last letter.
'ideal' with its last letter taken away is 'IDEA'.
'in' is the link.
(Other definitions for idea that I've seen before include "Thought or notion (4)" , "Plato's Form is" , "Intention" , "Brainwave" , "It comes to mind" .)