Show approval: no initial dissent (3)
I believe the answer is:
nod
'show approval' is the definition.
(I've seen this in another clue)
'no initial dissent' is the wordplay.
'initial' says to take the initial letters.
The first letter of 'dissent' is 'd'.
'no'+'d'='NOD'
(Other definitions for nod that I've seen before include "overlook something" , "slight bow" , "Land of exile" , "Agree non-verbally" , "sign of approval" .)