You need to be careful when one charges you money (5)
I believe the answer is:
rhino
I believe this is a double definition.
'you need to be careful when one charges you' is the first definition.
(rhinos charge at things)
'money' is the second definition.
(old-fashioned slang term for money)
(Other definitions for rhino that I've seen before include "When provoked, one may charge" , "Endangered species of large horned herbivore" , "Stumpy" , "Fierce beast (abbr.)" , "Horned pachyderm" .)