The most common and most likely answer to this crossword clue is the 10 letter word ADMONISHED
I've seen this crossword clue in The Guardian
A
D
M
O
N
I
S
H
E
D
Buddy explains!

The straight part
We know that "Warned" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warned = admonished.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 ADMONISHED mean?
ADMONISHED verb- To warn or notify of a fault; to reprove gently or kindly, but seriously; to exhort.
- To counsel against wrong practices; to caution or advise; to warn against danger or an offense; — followed by of, against, or a subordinate clause.
- To instruct or direct; to inform; to notify.