The most common and most likely answer to this crossword clue is the 9 letter word DETENTION
I've seen this crossword clue in The Daily Telegraph
D
E
T
E
N
T
I
O
N
More clues leading to the result DETENTION
- School punishment — what could make Eton end it?
- Prison‘s famous mounted guards went in without cover
- Confinement of Parisian number one trapped by heavy weight
- Ted in Eton suffering schoolboy punishment
- It need not upset confinement
- Intend to exact originally unusual punishment
- Confinement of French nervousness on air
- Desperately need tot in custody
Buddy explains!

The straight part
We know that "Confinement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case confinement = detention.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 DETENTION mean?
DETENTION noun- The act of detaining or the state of being detained.
- A temporary state of custody or confinement, especially of a prisoner awaiting trial, or of a student being punished.
- The bare physical control without the mental element of intention required for possession.