Put down top side perhaps (7)
I believe the answer is:
deposit
'put down' is the definition.
(I've seen this before)
'top side perhaps' is the wordplay.
'top side' becomes 'topside' (synonyms).
'perhaps' is an anagram indicator.
'topside' anagrammed gives 'DEPOSIT'.
(Other definitions for deposit that I've seen before include "Sum of money paid into a bank account" , "Money up front" , "Place" , "Put down or leave something" , "Sediment or bank lodgment" .)