Who might charge one money (5)

I believe the answer is:

rhino

I'm a little stuck... Click here to teach me more about this clue!

'one money' is the definition.
(old-fashioned slang term for money)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for rhino that I've seen before include "one still charges in Africa" , "When provoked, one may charge" , "Thick-skinned beast" , "big game" , "Hi, Ron! (anag)" .)

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app