Parable of small man in debt (5)
I believe the answer is:
sower
'parable' is the definition.
(as in the Parable of the Sower from the Bible)
'small man in debt' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'man in debt' becomes 'ower' (someone who owes money).
's'+'ower'='SOWER'
'of' is the link.
(Other definitions for sower that I've seen before include "One spreading seeds" , "One planting seeds" , "Broadcaster" , "Arable worker" , "Seedy operative" .)