The most common and most likely answer to this crossword clue is the 8 letter word BUTTONED
I've seen this crossword clue in The Daily Telegraph
B
U
T
T
O
N
E
D
More clues leading to the result BUTTONED
Buddy explains!

The straight part
We know that "Closed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case closed = buttoned.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 BUTTONED mean?
BUTTONED verb- To fasten with a button.
- To be fastened by a button or buttons.
- To stop talking.
- With buttons fastened