Overweight leader is an idiot (7)
I believe the answer is:
fathead
'an idiot' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'overweight leader' is the wordplay.
'overweight' becomes 'fat' (similar in meaning).
'leader' becomes 'head' (head is a kind of leader).
'fat'+'head'='FATHEAD'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for fathead that I've seen before include "Slang idiot with enlarged cranium?" , "Dimwit" , "Fool" , "silly ass!" , "Stupid person" .)