Almost perfect clue (4)
I believe the answer is:
idea
'clue' is the definition.
('I haven't a clue' means 'I have no idea')
'almost perfect' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'perfect' becomes 'ideal' (similar in meaning).
'ideal' with its final letter taken away is 'IDEA'.
(Other definitions for idea that I've seen before include "Light bulb above head" , "Intention" , "Fancy" , "Proposal" , "Sudden inspiration?" .)