Exposed weaknesses in principle (3)
I believe the answer is:
law
'principle' is the definition.
(thesaurus)
'exposed weaknesses' is the wordplay.
'exposed' means to look at the middle letters (outside letters removed).
'weaknesses' becomes 'flaws' (I've seen this before).
The middle letters of 'flaws' are 'LAW'.
'in' acts as a link.
(Other definitions for law that I've seen before include "Rule, statute" , "Official rule" , "Rule prohibiting certain actions" , "Rule imposed by authority" , "Collection of rules for a society" .)