Definition of "xorn"

Various monsters can tunnel through rock - either humanoid monsters with picks or rock eaters like rock moles and umber hulks; and some monsters like xorns and ghosts can pass through it without digging.

2002, David Damerell, “Where are they come from?[sic] ;)”, in rec.games.roguelike.development (Usenet)

Teleporting from an open room where there were a dozen black orcs firing bows at me and more pouring in through both doors a few nights ago didn't work the first two times, then when it did work it landed me, low on mana and hitpoints, in a room full of gnome mages who instantly summoned four umber hulks and a xorn!

2007, bear, “Makes Lovely Julienne Ogres....”, in rec.games.roguelike.angband (Usenet)

That afternoon, I summoned a Xorn—an earth elemental noted for its speed—and asked it to scout the caves of the Dragon's lair for me.

2010, Roger Bourke White, Rostov Rising: The Tales of Baron Rostov, page 229