Fit worker one providing gen (9)
I believe the answer is:
informant
'one providing gen' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'fit worker' is the wordplay.
'fit' becomes 'inform' (I've seen this before).
'worker' becomes 'ant' (worker is a type of ant).
'inform'+'ant'='INFORMANT'
Can you help me to learn more?
(Other definitions for informant that I've seen before include "Sneak" , "gives us the gen" , "Traitor" , "Telltale" , "source of intelligence" .)