Disapproving expression, and a sinister one (7)
I believe the answer is:
grimace
'disapproving expression' is the definition.
'grimace' can be an answer for 'expression' (I've seen this before). I'm unsure of the 'disapproving' bit.
'a sinister one' is the wordplay.
'a sinister' becomes 'grim' (I've seen this in another clue).
'one' becomes 'ace' (ace has a value of one in some card games).
'grim'+'ace'='GRIMACE'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for grimace that I've seen before include "displeasure" , "Expression of pain or disgust" , "Distortion of the face" , "Contort the face" , "Twisted facial expression" .)