Silent diplomacy securing independence (5)
I believe the answer is:
tacit
'silent' is the definition.
('tacit' can be a synonym of 'silent')
'diplomacy securing independence' is the wordplay.
'diplomacy' becomes 'tact' (I've seen this before).
'securing' is an insertion indicator.
'independence' becomes 'i'.
'tact' enclosing 'i' is 'TACIT'.
(Other definitions for tacit that I've seen before include "Implied without being stated" , "Respect, admiration" , "Understood without being directly expressed" , "without speaking" , "Implied -- inferred" .)