The most common and most likely answer to this crossword clue is the 7 letter word EXHORTS
E
X
H
O
R
T
S
Buddy explains!

The straight part
We know that "Warns" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warns = exhorts.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 EXHORTS mean?
EXHORTS verb- To urge; to advise earnestly.