Give new impetus to whistle-blower concerning silence (7)
I believe the answer is:
refresh
'give new impetus to' is the definition.
(to refresh is to to revitalise or give new purpose)
'whistle-blower concerning silence' is the wordplay.
'whistle blower' becomes 'ref' (I've seen this in other clues).
'concerning' becomes 're' (both can mean on a particular topic).
'silence' becomes 'sh' ('sh' is said to tell someone to be silent).
'ref'+'re'+'sh'='REFRESH'
(Other definitions for refresh that I've seen before include "cool" , "Restore strength and vigour as with food and drink" , "Give new strength to" , "Reinvigorate" , "perk up!" .)