The most common and most likely answer to this crossword clue is the 4 letter word SLOB
S
L
O
B
Buddy explains!
The straight part
We know that "chill out" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case chill out = slob.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 SLOB mean?
SLOB noun- A lazy and slovenly person.
- A lazy and obese person.