Almost perfect aim (4)
I believe the answer is:
idea
'aim' is the definition.
(idea is a kind of aim)
'almost perfect' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'perfect' becomes 'ideal' (similar in meaning).
'ideal' with its last letter taken off is 'IDEA'.
(Other definitions for idea that I've seen before include "Thought; concept" , "Flash of inspiration?" , "Notion in the mind" , "Notion, belief" , "Light bulb above head" .)