Philosophy of weak leader (8)
I believe the answer is:
thinking
'philosophy' is the definition.
(thesaurus)
'weak leader' is the wordplay.
'weak' becomes 'thin' ('thin' can be similar in meaning to 'weak').
'leader' becomes 'king' (King is an example**).
'thin'+'king'='THINKING'
'of' is the link.
(Other definitions for thinking that I've seen before include "Fancying" , "rationale" , "giving opinion" , "Take" , "consideration" .)