Soundly examine a bill of exchange (6)
I believe the answer is:
cheque
'a bill of exchange' is the definition.
(cheque is a kind of bill of exchange)
'soundly examine' is the wordplay.
'soundly' shows a homophone (sound like).
'examine' becomes 'check' (checking is a kind of examining).
'check' sounds like 'CHEQUE'.
(Other definitions for cheque that I've seen before include "Signed money order" , "A payment order form" , "Bank document" , "Means of payment" , "Bill of exchange" .)