Top side possibly put down (7)
I believe the answer is:
deposit
'put down' is the definition.
(I've seen this before)
'top side possibly' is the wordplay.
'top side' becomes 'topside' (synonyms).
'possibly' indicates anagramming the letters.
'topside' is an anagram of 'DEPOSIT'.
(Other definitions for deposit that I've seen before include "I posted (anag.)" , "Put money into a bank account" , "part-payment" , "(Money or mineral) put down" , "Returnable sum" .)