Variable income may create such desires (9)
I believe the answer is:
yearnings
'desires' is the definition.
(I know this)
'variable income' is the wordplay.
'variable' becomes 'y' (algebra).
'income' becomes 'earnings' (earnings is a kind of income).
'y'+'earnings'='YEARNINGS'
'may create such' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for yearnings that I've seen before include "Desires" , "wishes" .)