Moral rot in republic corrupted ... (13)
I believe the answer is:
incorruptible
'moral' is the definition.
(thesaurus)
'rot in republic corrupted' is the wordplay.
'corrupted' is an anagram indicator.
'rot'+'in'+'republic'='rotinrepublic'
'rotinrepublic' anagrammed gives 'INCORRUPTIBLE'.
(Other definitions for incorruptible that I've seen before include "Upright" , "Not subject to decay" , "Honest" , "Everlasting; unbribable" , "Proof against decay or bribery" .)