shale

From Middle English schale (“shell, husk; scale”), from Old English sċealu (“shell, husk, pod”), from Proto-West Germanic *skalu, from Proto-Germanic *skalō, from Proto-Indo-European *(s)kelH- (“to split, cut”), from *(s)kel- (“to split, cleave”). See also West Frisian skaal (“dish”), Dutch schaal (“shell”), schalie (“shale”), German Schale (“husk, pod”); also Lithuanian skalà (“splinter”), Old Church Slavonic скала (skala, “rock, stone”), Polish skała (“rock”), Albanian halë (“fish bone, splinter”), Sanskrit कल (kalá, “small part”); also Hittite [script needed] (iškalla, “to tear apart, slit open”), Lithuanian skélti (“to split”), Ancient Greek σκάλλω (skállō, “to hoe, harrow”).

出典: Wiktionary「shale」（CC BY-SA 4.0）