New pact EEC can sanction (10)
I believe the answer is:
acceptance
'sanction' is the definition.
(thesaurus)
'new pact eec can' is the wordplay.
'new' indicates an anagram.
'pact'+'eec'+'can'='pacteeccan'
'pacteeccan' anagrammed gives 'ACCEPTANCE'.
(Other definitions for acceptance that I've seen before include "Positive reply to invitation" , "Recognition" , "Consent" , "Modified Cape accent gets approval" , "Ability to tolerate" .)