Fierce person finally investing in bank (5)
I believe the answer is:
tiger
'fierce person' is the definition.
(I've seen this before)
'finally investing in bank' is the wordplay.
'finally' says to take the final letters.
'in' means one lot of letters goes inside another.
'bank' becomes 'tier' (I've seen this before).
The last letter of 'investing' is 'g'.
'g' put within 'tier' is 'TIGER'.
(Other definitions for tiger that I've seen before include "''... ... burning bright, in the forests of the night'' (Blake)" , "Striped carnivore" , "he got his stripes" , "Beast - type of 1 across" , "Cat; -- Woods" .)