The most common and most likely answer to this crossword clue is the 4 letter word WARN
I've seen this crossword clue in The Times
W
A
R
N
More clues leading to the result WARN
- Alert knight on board connected with conflict
- Make aware of danger of conflict
- Give notice of conflict over ending of immigration
- Tip off a Romeo to get into woman’s skirt
- Give advance notice of hostilities against Norway
- Admonish cricketer being vocal
- Following conflict, new alert
- Counsel is exhausted, we hear
- Caution of conflict with Navy
- Tip off white queen on board
Buddy explains!

The straight part
We know that "Make aware of danger" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case make aware of danger = warn.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 WARN mean?
WARN verb- To make (someone) aware of (something impending); especially:
- To caution or admonish (someone) against unwise or unacceptable behaviour.
- (chiefly with "off", "away", and similar words) To advise or order to go or stay away.
- To give warning.