The most common and most likely answer to this crossword clue is the 4 letter word PUNT
I've seen this crossword clue in The Times
P
U
N
T
Buddy explains!

The straight part
We know that "Money Irishman once used/flutter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case money irishman once used/flutter = punt.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 PUNT mean?
PUNT noun- A pontoon; a narrow shallow boat propelled by a pole.
- To propel a punt or similar craft by means of a pole.
- A kick made by a player who drops the ball and kicks it before it hits the ground.
- To dropkick; to kick something a considerable distance.
- To equivocate and delay or put off (answering a question, addressing an issue, etc).
- To retreat from one's objective; to abandon an effort one still notionally supports.
- To make the best choice from a set of non-ideal alternatives.
- A point in the game of faro.
- The act of playing at basset, baccara, faro, etc.
- A bet or wager.
- Gambling, as a pastime, especially betting on horseraces or the dogs.
- A highly speculative investment or other commitment.
- A wild guess.
- An indentation in the base of a wine bottle.
- A thin glass rod which is temporarily attached to a larger piece in order to better manipulate the larger piece.
- To play at basset, baccara, faro, etc.
- To stake against the bank, to back a horse, to gamble or take a chance more generally
- To make a highly speculative investment or other commitment, or take a wild guess.
- The Irish pound, used as the unit of currency of Ireland until it was replaced by the euro in 2002.