Acetic acid (7)
I believe the answer is:
vinegar
'acetic acid' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for vinegar that I've seen before include "Liquid used as condiment or food preservative" , "Pickling condiment" , "Ill-temper" , "acidic stuff" , "Peevishness" .)