The most common and most likely answer to this crossword clue is the 5 plus 5 letter word SILLY MONEY
I've seen this crossword clue in The Times
S
I
L
L
Y
M
O
N
E
Y
Buddy explains!
The straight part
We know that "A bomb," is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a bomb, = silly money.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.