Etymon
enm-regretten-english-regret-protoindoeuropean-pleh1-protoindoeuropean-nos-protoindoeuropean-plh1nos-protogermanic-fullaz-protogermanic-fullaz-old-english-ful-middle-english-ful-english-ful-english-regretful-protoindoeuropean-leyg-protogermanic-likader
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.