Almost perfect vision (4)
I believe the answer is:
idea
'vision' 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 "It comes to mind" , "Proposal" , "Sudden inspiration?" , "Plan" , "A suspicion of" .)