Disapproving expressions and sinister ones (8)
I believe the answer is:
grimaces
'disapproving expressions' is the definition.
'sinister ones' is the wordplay.
'sinister' becomes 'grim'.
'ones' becomes 'aces' ('ace' can be a synonym of 'one').
'grim'+'aces'='GRIMACES'
'and' is the link.
(Other definitions for grimaces that I've seen before include "Contorted facial expressions" , "threatening features" , "Facial distortions of distaste" , "Contortion of face, perhaps expressing pain" , "Twisted expressions" .)