Not a reticent bank employee (6)
I believe the answer is:
teller
'bank employee' is the definition.
(as in a bank teller)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for teller that I've seen before include "Bank cashier or narrator of story" , "who worked on the hydrogen bomb" , "Narrator and bank clerk" , "Bank official to narrate the story" , "one gives relation" .)