As nouns the difference between martyr and selflessness
is that
martyr is one who willingly accepts being put to death for adhering openly to one's religious beliefs; notably, saints canonized after martyrdom while
selflessness is the quality or state of being selfless.
As a verb martyr
is 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.