Etymon
gem-roana-protoindoeuropean-ter-protoindoeuropean-trom-protogermanic-ra-protogermanic-rora-protowest-germanic-ror-old-english-roor-middle-english-rother-english-rudder-protoindoeuropean-h1egh-protoindoeuropean-s-protoindoeuropean-h1eghs-protoitalic-eks-latin-ex-latin-ex-protoindoeuropean-h1lengwh-protoindoeuropean-us-protoindoeuropean-h1lenghusder
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.