Source of interest, you said with more confidence (6)
I believe the answer is:
usurer
'source of interest' is the definition.
(a usurer charges interest on loans)
'you said with more confidence' is the wordplay.
'said' shows a homophone (sound like).
'with more confidence' becomes 'surer' (more sure or confident).
'you' sounds like 'u'.
'u'+'surer'='USURER'
(Other definitions for usurer that I've seen before include "One who charges undue interest" , "Businessman taking a lot of interest" , "Lender at an exorbitant rate" , "Moneylender who charges exorbitant rates" , "He expects lots of interest" .)