Pieces of eight for Long John? (6)

I believe the answer is:

silver

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

'long john?' is the definition.
(I've seen this in another clue)

I can't explain the rest of the clue.

(Other definitions for silver that I've seen before include "Argent" , "Pirate" , "Older regular internet user" , "Sliver of precious metal" , "Movies" .)

I've seen this clue in The Sun.

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