Etymon
pie-ne-protoindoeuropean-n-protogermanic-un-protowest-germanic-un-old-english-un-middle-english-un-english-un-protoitalic-merks-latin-merx-latin-mercor-latin-mercantem-italian-mercante-latin-ilemder
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.