donderblad.

From Middle Dutch donderblat, with a by-form donderbaert (whence the modern obsolete synonym donderbaard). By surface analysis, donder (“thunder”) + blad (“leaf”), perhaps from a folk belief that these plants protected against thunder (as they were commonly planted on roofs: compare the synonyms huislook, daklook and other variants, as well as the taxonomic name, tēctōrum meaning "of roofs"). If donderbaert (attested also in German Donnerbart) is the original form underlying donderblat, it may be compared with French joubarbe (“houseleek”), from Latin Iovis barba (or barba Iovis) which literally means Jupiter's beard. If this association is correct, the word could be viewed as a calque of the Latin, with donder referring to the Germanic thunder god similar to how diēs Iovis was calqued into the Germanic languages using this deity's name (see the etymology at donderdag). The original meaning would then be "Donar's beard".