Foreign coin sent round as a deposit (8)
I believe the answer is:
sediment
'a deposit' is the definition.
(synonyms)
'foreign coin sent round' is the wordplay.
'foreign coin' becomes 'dime' (I've seen this before).
'round' is an insertion indicator.
'dime' put into 'sent' is 'SEDIMENT'.
'as' acts as a link.
(Other definitions for sediment that I've seen before include "Grounds - debris" , "Matter sinking to the bottom of a liquid" , "Deposit at the bottom of a liquid" , "Lees" , "Silt" .)