Tenant's deposit -- source of rancour (6)
I believe the answer is:
lodger
'tenant's' is the definition.
(lodger is a kind of tenant)
'deposit source of rancour' is the wordplay.
'deposit' becomes 'lodge' ('lodge' can be a synonym of 'deposit').
'source of rancour' becomes 'r' (I can't explain this - if you can you should believe this answer much more).
'lodge'+'r'='LODGER'
Can you help me to learn more?
(Other definitions for lodger that I've seen before include "Boarder" , "Renter of rooms" , "One who lives in a hired room" , "Renter living with owner" , "Long-term paying guest" .)