The most common and most likely answer to this crossword clue is the 8 letter word COMATOSE
I've seen this crossword clue in Financial Times
C
O
M
A
T
O
S
E
More clues leading to the result COMATOSE
- Extremely drowsy mother in bed, oddly ousted
- Out to sea, drifting behind Commodore
- Comes to a settlement while unconscious
- Qualification keeping headless fruit inert
- Unconscious, comes to – a development
- Characteristic of a kipper?
- Excited, as to come out
- Arrive carrying a drunkard back in a sleepy state
- Firm very large in China becoming dormant?
- Out cold, come to as arranged
Buddy explains!

The straight part
We know that "inert" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case inert = comatose.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 COMATOSE mean?
COMATOSE adjective- In a coma: unconscious.
- Drowsy or lethargic.
- Fast asleep.