Convinced India and China in secret (14)
I believe the answer is:
confidentially
'secret' is the definition.
(thesaurus)
'convinced india and china' is the wordplay.
'convinced' becomes 'confident' (conviction is confidence something is true).
'india' becomes 'i' (phonetic alphabet: alpha, bravo, charlie etc.).
'and' says to put letters next to each other.
'china' becomes 'ally' (I've seen this in other clues).
'confident'+'i'+'ally'='CONFIDENTIALLY'
'in' acts as a link.
(Other definitions for confidentially that I've seen before include "behind closed doors" , "with no one to overhear" .)