Sinclair returned carrying a bit of Iranian cash (4)
I believe the answer is:
rial
'iranian cash' is the definition.
(currency of Iran)
'sinclair returned carrying a bit' is the wordplay.
'sinclair' becomes 'lar' (I can't justify this - if you can you should give a lot more credence to this answer).
'returned' is a reversal indicator.
'carrying' indicates putting letters inside.
'a bit' becomes 'i' (resembles l, a binary digit or bit).
'lar' in reverse letter order is 'ral'.
'ral' enclosing 'i' is 'RIAL'.
'of' is the link.
Can you help me to learn more?
(Other definitions for rial that I've seen before include "Middle Eastern money" , "Unit of money in Iran, like lira" , "Cash" , "Monetary unit of Iran" , "Ready" .)