Fierce person keeping grand in bank (5)
I believe the answer is:
tiger
'fierce person' is the definition.
(tiger can mean a ferocious or fierce person)
'grand in bank' is the wordplay.
'grand' becomes 'g' (G is short for grand as in a thousand).
'in' is an insertion indicator.
'bank' becomes 'tier' (both can mean a row of similar things).
'g' going inside 'tier' is 'TIGER'.
'keeping' acts as a link.
(Other definitions for tiger that I've seen before include "Wildcat of Bengal" , "Formidable opponent" , "Fierce, determined type" , "Carnivorous large cat" , "he got his stripes" .)