The most common and most likely answer to this crossword clue is the 8 letter word LYING-IN
I've seen this crossword clue in Financial Times
L
Y
I
N
G
-
I
N
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 = lying-in.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 LYING-IN mean?
LYING-IN noun- The final stages of pregnancy; accouchement.
- A period of postpartum confinement, typically a month or longer, formerly common in Europe and still practiced in some parts of the world.
- Of, or relating to childbirth or postpartum confinement