Deposit this beside the river (4)
I believe the answer is:
bank
'deposit' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for bank that I've seen before include "Financial institution - riverside" , "River side - pool" , "River's edge" , "Row" , "Long mound; rely (on)" .)