Everyone plus one in sea on piece of jewellery (9)

I believe the answer is:

medallion

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'piece of jewellery' is the definition.
'medallion' can be an answer for 'piece' (I have seen 'piece of meat' mean 'medallion' so perhaps 'piece' could also mean 'medallion'). I am not sure about the 'of jewellery' bit.

'everyone plus one in sea on' is the wordplay.
'everyone' becomes 'all' (all people).
'plus' is a charade indicator (letters next to each other).
'one' becomes 'I' (Roman numeral).
'in' is an insertion indicator.
'sea' becomes 'med' (short for Mediterranean).
'all'+'i'='alli'
'med'+'on'='medon'
'alli' placed inside 'medon' is 'MEDALLION'.

Can you help me to learn more?

(Other definitions for medallion that I've seen before include "Metal disc" , "Ornamental disc on a chain" , "Cut" , "Decoration worn round the neck" , "Circular piece of meat - commemorative award" .)

I've seen this clue in The Daily Express.

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