The most common and most likely answer to this crossword clue is the 9 letter word HALFPENNY
I've seen this crossword clue in The Times
H
A
L
F
P
E
N
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Y
More clues leading to the result HALFPENNY
Buddy explains!
The straight part
We know that "old money" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old money = halfpenny.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HALFPENNY mean?
HALFPENNY noun- (plural: halfpennies) A discontinued British coin worth half of one penny (old or new).
- (plural: halfpence) A quantity of money worth half a penny.
- Costing or worth one halfpenny.