The most common and most likely answer to this crossword clue is the 9 letter word GREENBACK
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Buddy explains!

The straight part
We know that "(dollar) bill" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case (dollar) bill = greenback.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 GREENBACK mean?
GREENBACK noun- Any bill that is legal tender in the US (originally printed with green and black ink) issued by the Federal Reserve.
- The United States dollar.
- A unit of American currency issued during the Civil War by the Treasury Department.