One flipping expression of disgust is sufficient (6)
I believe the answer is:
enough
'sufficient' is the definition.
('enough' can be similar in meaning to 'sufficient')
'one flipping expression of disgust' is the wordplay.
'flipping' shows that the letters should be reversed in order.
'expression of disgust' becomes 'ugh' (I've seen this before).
'one' backwards is 'eno'.
'eno'+'ugh'='ENOUGH'
'is' is the link.
(Other definitions for enough that I've seen before include "Adequate amount to meet the purpose" , "This is going no further!" , "To the required degree" , "Sufficient to answer demand" , "satisfying" .)