Said it’s an incentive for a lightweight (5)
I believe the answer is:
carat
'a lightweight' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'said it's an incentive' is the wordplay.
'said' shows a homophone (sound like).
'it's an incentive' becomes 'carrot' (as in a carrot and stick).
'carrot' sounds like 'CARAT'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for carat that I've seen before include "Weight of ice" , "Gemstone weight unit" , "Not a large weight" , "Unit for precious stone weights" , "Metal weight" .)