The most common and most likely answer to this crossword clue is the 8 letter word INACTIVE
I've seen this crossword clue in The Daily Telegraph
I
N
A
C
T
I
V
E
More clues leading to the result INACTIVE
- Idle one on green encircling court
- When disturbed, I can't — I have to be doing nothing
- Still it gets held up in unfortunate cave-in
- Trials take place here shortly — one has to be still
- Still popular, concert leader in uplifting musical
- Nutmeg caught in local doing nothing
- During performance I have to be quiet
- Resting during performance, wives will be undressed
- Idle at home, one taking in ITV broadcast
- Sluggish, local inhabitant having caught cold on island
Buddy explains!

The straight part
We know that "Idle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case idle = inactive.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 INACTIVE mean?
INACTIVE adjective- Not active, temporarily or permanently.
- Not functioning or operating; broken down
- Retired from duty or service.
- Relatively inert.
- Showing no optical activity in polarized light.