Illicit rice contains this acid (6)
I believe the answer is:
citric
'this acid' is the definition.
(citric acid is a kind of acid)
'illicit rice contains' is the wordplay.
'contains' indicates the answer is hidden within the clue.
'CITRIC' is hidden in the letters of 'illicit rice'.
(Other definitions for citric that I've seen before include "Derived from oranges, lemons, etc" , "Derived from eg, lemon" , "Derived from, eg, lemons" , "Acid, from lemons say" , "Lemony" .)