Money bag is clean, containing old shilling (5)
I believe the answer is:
purse
'money bag' is the definition.
(I've seen this before)
'clean containing old shilling' is the wordplay.
'clean' becomes 'pure' (similar in meaning).
'containing' indicates putting letters inside.
'old shilling' becomes 's' (abbreviation e.g. Lsd - pounds, shillings, pence. I am not sure about the 'old' bit.).
'pure' placed around 's' is 'PURSE'.
'is' is the link.
Can you help me to learn more?
(Other definitions for purse that I've seen before include "bag for loose change" , "Contract, crease" , "Super (anag.)" , "amount of money" , "Winner's prize" .)