One having shot janitor finally enters bank (5)
I believe the answer is:
trier
'one having shot' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'janitor finally enters bank' is the wordplay.
'finally' says to take the final letters.
'enters' indicates putting letters inside.
'bank' becomes 'tier' (both can mean a row of similar things).
The last letter of 'janitor' is 'r'.
'r' going into 'tier' is 'TRIER'.
Can you help me to learn more?
(Other definitions for trier that I've seen before include "One who refuses to give up -- German city on the Moselle" , "Judge perhaps" , "European city" , "Persevering type" , "Judge, say" .)