The most common and most likely answer to this crossword clue is the 7 letter word FORGERY
I've seen this crossword clue in The Sunday Telegraph
F
O
R
G
E
R
Y
Buddy explains!
The straight part
We know that "making money illegally" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case making money illegally = forgery.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 FORGERY mean?
FORGERY noun- The act of forging metal into shape.
- The act of forging, fabricating, or producing falsely; especially the crime of fraudulently making or altering a writing or signature purporting to be made by another, the false making or material alteration of or addition to a written instrument for the purpose of deceit and fraud.
- That which is forged, fabricated, falsely devised or counterfeited.
- An invention, creation.