As a serf, he had a fortune (5)
I believe the answer is:
helot
'as a serf he had a fortune' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he had a fortune' is the wordplay.
'had' means one lot of letters go next to another.
'a fortune' becomes 'lot' (as in a person's lot in life).
'he'+'lot'='HELOT'
Can you help me to learn more?
(Other definitions for helot that I've seen before include "He's bound to land" , "Spartan serf" , "Hotel (anag) - serf" , "Serf of ancient Sparta" , "downtrodden?" .)