Charlie, a comparatively mousy employee in bank (7)
I believe the answer is:
cashier
'employee in bank' is the definition.
'charlie a comparatively mousy' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'comparatively mousy' becomes 'shier' (mousy can mean shy).
'c'+'a'+'shier'='CASHIER'
(Other definitions for cashier that I've seen before include "Discharge" , "Dismiss (someone) from the armed forces in disgrace" , "Bank clerk" , "Sack" , "person taking the money" .)