Crossword Genius

Word used in pricing a period piece

Ross

I believe the answer is:

per

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'word used' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'pricing a period piece' is the wordplay.
'pricing a period' becomes 'pe' (I can't justify this - if you can you should give a lot more credence to this answer).
'piece' becomes 'r' (abbreviation for Rook).
'pe'+'r'='PER'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for per that I've seen before include "Preposition meaning for each" , "For each or every" , "Preposition indicating by means of" , "According to" .)

I've seen this clue in the Evening Standard.
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