Write letters to coppers (3)
I believe the answer is:
pen
'write' is the definition.
(synonyms)
'letters to coppers' is the wordplay.
'letters' becomes 'en' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to' means one lot of letters go next to another (I've seen this in other clues).
'coppers' becomes 'p'.
'en' put after 'p' is 'PEN'.
Can you help me to learn more?
(Other definitions for pen that I've seen before include "record" , "Coop" , "Shut up" , "Prison" , "Cage - bird" .)