Just to get it more specific: "Yliakum" is only the world inside the stalactite, and most inhabitants may not know (for certain) that there is something outside, and even the stalactite appears only as one possible theory to them? In this case it may not be a big surprise that they may not have a very common name for "the cave surrounding Yliakum". Not to mention even "the planet around the cave", beyond the Stone Labyrinth leading to its surface.