The most common and most likely answer to this crossword clue is the 4 letter word KIST
K
I
S
T
More clues leading to the result KIST
Buddy explains!

The straight part
We know that "coffin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coffin = kist.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 KIST mean?
KIST verb- To touch with the lips or press the lips against, usually to show love or affection or passion, or as part of a greeting.
- To (cause to) touch lightly or slightly; to come into contact.
- Of two or more people, to touch each other's lips together, usually to express love or affection or passion.
- To treat with fondness.
- A chest.
- A coffin.
- To place in a coffin.