Bank employee who can't keep his mouth shut? (6)
I believe the answer is:
teller
'bank employee' is the definition.
(as in a bank teller)
I cannot 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 official to narrate the story" , "one gives relation" , "Cashier - vote counter - narrator" , "One introducing relation" , "Bank official or reporter" .)