Practically perfect plan (4)
I believe the answer is:
idea
'plan' is the definition.
(both can mean an intention)
'practically perfect' is the wordplay.
'practically' means to remove the last letter.
'perfect' becomes 'ideal' (similar in meaning).
'ideal' with its final letter removed is 'IDEA'.
(Other definitions for idea that I've seen before include "intellectual product" , "Thought or notion (4)" , "Intention" , "Something imagined in the mind" , "Notion in the mind" .)