Confident when taken to court about source of revenue (7)
I believe the answer is:
assured
'confident' is the definition.
('assured' can be similar in meaning to 'confident')
'when taken to court about source of revenue' is the wordplay.
'when' becomes 'as'.
'taken to court' becomes 'sued' ('sue' can be a synonym of 'take to court').
'about' indicates putting letters inside.
'source of' suggests taking the first letters.
The first letter of 'revenue' is 'r'.
'sued' going around 'r' is 'sured'.
'as'+'sured'='ASSURED'
(Other definitions for assured that I've seen before include "Gave confidence to" , "Self-confident" , "without doubt" , "Informed with certainty and confidence" , "Confident and self-possessed" .)