From Middle English sclabbe, slabbe, of uncertain origin; possibly from *slap, related to dialectal slappel (“portion, piece”), along with slape (“slippery”), sleip (“smooth piece of timber”), borrowed through Old Norse sleipr from Proto-Germanic *slaipaz, from Proto-Indo-European *(s)leyb-. See also Norwegian sleip (“slippery”) and Icelandic sleipur.