Let off steam after The Sun is in the black (7)
I believe the answer is:
solvent
'is in the black' is the definition.
(both can mean having enough money to pay debts)
'let off steam after ithe' is the wordplay.
'let off steam' becomes 'vent' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'ithe' becomes 'sol' (I am not sure about this - if you are sure you should believe this answer much more).
'vent' after 'sol' is 'SOLVENT'.
'suni' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for solvent that I've seen before include "In credit" , "Not bankrupt" , "water, for example?" , "Capable of paying all debts" , "Financially sound" .)