Thought almost perfect (4)
I believe the answer is:
idea
'thought' is the definition.
(I know that thought can be written as idea)
'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 away is 'IDEA'.
(Other definitions for idea that I've seen before include "Product of the mind" , "Creative spark" , "Something imagined in the mind" , "It comes to mind" , "Thought, belief" .)