Almost perfect plan (4)
I believe the answer is:
idea
'plan' is the definition.
(both can mean an intention)
'almost perfect' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'perfect' becomes 'ideal' (similar in meaning).
'ideal' with its final letter removed is 'IDEA'.
(Other definitions for idea that I've seen before include "It comes to mind" , "Notion, belief" , "Thought, belief" , "Creative spark" , "Sudden inspiration?" .)