Almost perfect concept (4)
I believe the answer is:
idea
'concept' 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 last letter taken off is 'IDEA'.
(Other definitions for idea that I've seen before include "Notion, image" , "Clue" , "Purpose" , "Plan" , "Creative spark" .)