The most common and most likely answer to this crossword clue is the 5 letter word CHAFE
I've seen this crossword clue in Financial Times
C
H
A
F
E
More clues leading to the result CHAFE
Buddy explains!

The straight part
We know that "Warm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warm = chafe.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 CHAFE mean?
CHAFE noun- Heat excited by friction.
- Injury or wear caused by friction.
- Vexation; irritation of mind; rage.
- An expression of opinionated conflict.
- To excite heat in by friction; to rub in order to stimulate and make warm.
- To excite passion or anger in; to fret; to irritate.
- To fret and wear by rubbing.
- To rub; to come together so as to wear by rubbing; to wear by friction.
- To be worn by rubbing.
- To have a feeling of vexation; to be vexed; to fret; to be irritated.