The most common and most likely answer to this crossword clue is the 5 plus 4 letter word ALARM BELL
I've seen this crossword clue in Financial Times
A
L
A
R
M
B
E
L
L
More clues leading to the result ALARM BELL
- Warning: a large branch by our cartoonist
- Warning everyone about cracking marble
- A batter collecting runs, cricketer Warner
- One ringing to warn you of danger?
- A tricky ramble by two lakes – one sounds a warning
- An aborted escapade — two students snatching decoration – results in warning
- . Warning signal as marble arch blocks everything
- Buzzer gives a large projection to account for low loss at the beginning
- Alert everyone about weapon — live and loaded, primarily
Buddy explains!
The straight part
We know that "Warning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warning = alarm bell.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.