Of uncertain origin; proposed derivations include:
* From a Proto-Indo-European root common to Ancient Greek λίθος (líthos, “stone”), λίστρον (lístron, “spade, shovel”) and Latvian lîžu (“to clear a land”). By dint of mentioning only this theory, De Vaan appears to tentatively favor this theory, albeit with heavy doubts.
* From Proto-Indo-European *slaid-, *sled-, a root common to Proto-Germanic *slītaną (“to tear apart”).
* From a Proto-Indo-European root common to Old Norse lesta (“to damage”), lǫstr (“damage”) and Ancient Greek λαιδρός (laidrós, “bold”).
* From Proto-Indo-European *deh₂y-dʰeh₁-e/o- (“to put in one's share”), a compound of *deh₂y- + *dʰeh₁-.