The most common and most likely answer to this crossword clue is the 9 letter word WIDOWHOOD
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Buddy explains!
The straight part
We know that "After marriage vow, with husband buried in box, perhaps, the state one’s in?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case after marriage vow, with husband buried in box, perhaps, the state one’s in? = widowhood.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 WIDOWHOOD mean?
WIDOWHOOD noun- The state or period of being a widow or widower.