Exorbitancy sees spent ruination (9)
I believe the answer is:
'exorbitancy' is the definition.
I can't judge whether this defines the answer.
'sees spent ruination' is the wordplay.
'ruination' indicates an anagram (the letters are ruined).
'seesspent' is an anagram of 'STEEPNESS'.
Can you help me to learn more?
(Another definition for steepness that I've seen is " Gradient".)