Plan almost perfect (4)
I believe the answer is:
idea
'plan' is the definition.
(thesaurus)
'almost perfect' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'perfect' becomes 'ideal' ('ideal' can be similar in meaning to 'perfect').
'ideal' with its final letter taken away is 'IDEA'.
(Other definitions for idea that I've seen before include "Fancy" , "Creative spark" , "Something imagined in the mind" , "Inkling" , "Flash of inspiration?" .)