The most common and most likely answer to this crossword clue is the 6 letter word MARTYR
I've seen this crossword clue in The Times
M
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More clues leading to the result MARTYR
- Maybe Thomas More's pretentious title captivates
- Male, culturally pretentious Republican, one who died for cause
- Good man killed after reversing railway vehicle
- Try arm wrestling victim
- Person sacrificed sheep the wrong way
- . Harm novice displaying no love for saint?
- Two queens, one over time a victim of her faith
- For example, Sebastian Drive, backing onto ancient city
- Oscar-winning film: King Sebastian
- TV commentator hugs disheartened Conservative who may have got stoned
Buddy explains!

The straight part
We know that "one who died for cause" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one who died for cause = martyr.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 MARTYR mean?
MARTYR noun- One who willingly accepts being put to death for adhering openly to one's religious beliefs; notably, saints canonized after martyrdom.
- (by extension) One who sacrifices his or her life, station, or something of great personal value, for the sake of principle or to sustain a cause.
- (with a prepositional phrase of cause) One who suffers greatly and/or constantly, even involuntarily.
- To make someone into a martyr by putting him or her to death for adhering to, or acting in accordance with, some belief, especially religious; to sacrifice on account of faith or profession.
- To persecute.
- To torment; to torture.