Regret concealing steady income (7)
I believe the answer is:
revenue
'income' is the definition.
(I know that income can be written as revenue)
'regret concealing steady' is the wordplay.
'regret' becomes 'rue' (to rue something is to regret it).
'concealing' is an insertion indicator.
'steady' becomes 'even' (associated in meaning).
'rue' enclosing 'even' is 'REVENUE'.
(Other definitions for revenue that I've seen before include "Money received" , "Government's income" , "Return" , "Gross business income" , "Income from tax" .)