Etymon
gem-slepaz-protowest-germanic-slap-protoindoeuropean-kos-protogermanic-gaz-protowest-germanic-g-protowest-germanic-slapag-old-english-slpig-middle-english-slepy-english-sleepy-english-eepy-clipping-of-sleepy
A dedicated page for this root is on the way — it will gather every word descended from it, sibling forms across daughter languages, and a branching map of the family tree.