Vinegar gives expert twitch (6)
I believe the answer is:
acetic
'vinegar gives expert twitch' is the definition.
I can't tell whether this defines the answer.
'expert twitch' is the wordplay.
'expert' becomes 'ace' (ace is a kind of expert).
'twitch' becomes 'tic' (tic is a kind of twitch).
'ace'+'tic'='ACETIC'
Can you help me to learn more?
(Other definitions for acetic that I've seen before include "tart" , "really sour" , "Like vinegar's acid" , "Like the acid in vinegar" , "sort of acid" .)