Thought to be perfect, though reduced by a pound (4)
I believe the answer is:
idea
'thought' is the definition.
(synonyms)
'though reduced by a pound' is the wordplay.
'though' becomes 'if' (I've seen this in other clues).
'reduced' means to remove the last letter.
'by' means one lot of letters go next to another.
'a pound' becomes 'dea' (I can't explain this - if you can you should believe this answer much more).
'if' with its last letter taken away is 'i'.
'i'+'dea'='IDEA'
'to be perfect' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for idea that I've seen before include "Creative spark" , "Product of the mind" , "Fancy" , "Notion in the mind" , "It comes to mind" .)