@A_C_McGregor @goatsarah This does get confusing (although my brain is not in tiptop operation today). Wiktionary lists marline < MLGer marling < MDutch marlijn (“cord”) < marlen (“secure, fasten”), frequentative of maren (“to moor”) < Proto-Germanic *mairōną (“to moor, fasten to”), from PIE *mer-. But for the cover meaning of marl it has < ME marle < OFr marle, < LL margila, diminutive of marga (“marl”). I may have to find a real dictionary.