Knight detaining old silly wants gold coin (8)

I believe the answer is:

doubloon

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'coin' is the definition.
(doubloon is a kind of coin)

'knight detaining old silly wants gold' is the wordplay.
'knight' becomes 'dub' (to dub can mean to knight someone).
'detaining' means one lot of letters goes inside another.
'old' becomes 'o' (abbreviation).
'silly wants gold' becomes 'loon' (I can't justify this - if you can you should believe this answer much more).
'dub' enclosing 'o' is 'doub'.
'doub'+'loon'='DOUBLOON'

Can you help me to learn more?

(Other definitions for doubloon that I've seen before include "Another old Spanish coin" , "Former Spanish gold coin" , "Ancient Spanish gold coin" , "Old Spanish gold coin" .)

I've seen this clue in The Sun.

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