A jam that may have onions in it! (6)

I believe the answer is:

pickle

I'm a little stuck... Click here to teach me more about this clue!

'a jam' is the definition.
(I know that jam can be written as pickle)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for pickle that I've seen before include "A preserved vegetable or a fine mess" , "Relish; tricky situation" , "Jam - vegetables preserved in vinegar or brine" , "Preserve; muddle" , "Relish; predicament" .)

I've seen this clue in The Globe and Mail.

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