The most common and most likely answer to this crossword clue is the 6 letter word EXPIRE
E
X
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More clues leading to the result EXPIRE
Buddy explains!

The straight part
We know that "die" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case die = expire.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 EXPIRE mean?
EXPIRE verb- To die.
- To lapse and become invalid.
- To exhale; to breathe out.
- To give forth insensibly or gently, as a fluid or vapour; to emit in minute particles.
- To bring to a close; to terminate.