Old fashioned jug, or maybe porridge, termed vile (7)

I believe the answer is:

durance

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'old' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for durance that I've seen before include "Imprisonment" , "confinement no longer?" , "River in southern France" , "being kept in prison, in the past" .)

I've seen this clue in the Evening Standard.

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