Etymon
pie-dherg-protoindoeuropean-dhergos-protogermanic-derkaz-protowest-germanic-derk-old-english-deorc-middle-english-derk-english-dark-protoindoeuropean-h2elder
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.