Coppers write letters! (5)

I believe the answer is:

pence

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'coppers' is the definition.
(I've seen this before)

'write letters' is the wordplay.
'write' becomes 'pen' (synonyms).
'letters' becomes 'ce' (I can't justify this - if you can you should give a lot more credence to this answer).
'pen'+'ce'='PENCE'

Can you help me to learn more?

(Other definitions for pence that I've seen before include "Small quantity of money" , "Old coins" , "Fractions of a pound" , "''... fumble in a greasy till/and add the halfpence to the ...'' (Yeats)" , "offering to St Peter" .)

I've seen this clue in the Evening Standard.

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