Acetic acid in grave trouble (7)
I believe the answer is:
vinegar
'acetic acid' is the definition.
(I've seen this before)
'in grave trouble' is the wordplay.
'trouble' is an anagram indicator.
'in'+'grave'='ingrave'
'ingrave' anagrammed gives 'VINEGAR'.
(Other definitions for vinegar that I've seen before include "Sour-tasting liquid as condiment" , "Ill-temper" , "bad wine?" , "Liquid used as condiment or food preservative" , "Condiment - bad temper" .)