A jam, oddly enough (6)
I believe the answer is:
pickle
'a jam' is the definition.
(synonyms)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for pickle that I've seen before include "Relish; preserve" , "Relish; predicament" , "Veg or fruit relish" , "Preserve; mess" , "Jam - vegetables preserved in vinegar or brine" .)