In grave trouble certainly in a pickle (7)
I believe the answer is:
vinegar
'pickle' is the definition.
(thesaurus)
'in grave trouble' is the wordplay.
'trouble' indicates an anagram.
'in'+'grave'='ingrave'
'ingrave' anagrammed gives 'VINEGAR'.
'certainly in a' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for vinegar that I've seen before include "Ill-temper" , "bad wine?" , "Pickling medium" , "Sourish liquid for flavouring chips" , "Soured wine, cider etc." .)