The most common and most likely answer to this crossword clue is the 2 plus 4 letter word AT REST
I've seen this crossword clue in Independent
A
T
R
E
S
T
More clues leading to the result AT REST
- Not moving beside others
- Not moving theatre’s two shows
- Relaxing in an exam covering one of the three basics?
- Middle of day, time to stand still
- Still relaxing
- Stopped king interrupting a challenge
- Still in the theatre stalls
- Still a strain? That’s about right
- Runs into an exam, being late
- Still treats to distribute
Buddy explains!

The straight part
We know that "being late" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being late = at rest.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.