Rob turned up with oarsman - one's lent money (8)
I believe the answer is:
borrower
'one's lent money' is the definition.
I can't judge whether this defines the answer.
'rob turned up with oarsman' is the wordplay.
'turned up' is a reversal indicator.
'with' means one lot of letters go next to another.
'oarsman' becomes 'rower' (synonyms).
'rob' backwards is 'bor'.
'bor'+'rower'='BORROWER'
Can you help me to learn more?
(Other definitions for borrower that I've seen before include "One having interest" , "One intends to return things" , "Neither this nor a lender be, they say" , "Debtor" , "one temporarily in debt" .)