Rashi on Genesis 50:10/רש"י על בראשית נ׳:י׳

1גרן האטד THE THRESHING FLOOR OF ATAD — It was so called because it was surrounded by a hedge of (אטדין) thorns (not because thorns were threshed there) Our Rabbis explained that it was so called in consequence of an incident that occurred there — that all the kings of Canaan and the princes of Ishmael came to wage war against them, but as soon as they saw Joseph’s crown hanging over Jacob’s coffin they all rose and hung their crowns on it and thus wreathed it with crowns like a threshing floor that is surrounded with a hedge of thorns (Sotah 13a).