Crossword Genius

Old jail bird, not quite silver (5)

Ross

I believe the answer is:

gulag

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

'old jail' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

'bird not quite silver' is the wordplay.
'bird' becomes 'gull' (gull is a kind of bird).
'not quite' means to remove the last letter.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'gull' with its final letter taken off is 'gul'.
'gul'+'ag'='GULAG'

Can you help me to learn more?

(Other definitions for gulag that I've seen before include "penal system" , "Place for political dissidents" , "place of detention" , "Soviet camps for dissidents" , "Russian prison camp for political prisoners" .)

I've seen this clue in The Guardian.
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