One posted in Picardy? (4)

I believe the answer is:

card

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'one' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'posted in picardy?' is the wordplay.
'posted in' indicates the answer is hidden within the clue.
'CARD' is hidden within 'picardy'.

Can you help me to learn more?

(Other definitions for card that I've seen before include "Amusing person" , "Comic" , "Stiff paper; comb" , "Eccentric - stiff paper" , "Something players try to avoid" .)

I've seen this clue in the Evening Standard.

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