Write about crime, ultimately, for coppers (5)
I believe the answer is:
pence
'coppers' is the definition.
(coppers can mean copper coins)
'write about crime ultimately' is the wordplay.
'write' becomes 'pen' (synonyms).
'about' becomes 'c' (circa).
'ultimately' indicates one should take the final letters.
The final letter of 'crime' is 'e'.
'pen'+'c'+'e'='PENCE'
'for' is the link.
(Other definitions for pence that I've seen before include "Money used to be pounds, shillings and ....." , "Small change" , "Old coins" , "Small coins" , "offering to St Peter" .)