Meaning

noun tall North American perennial with creeping rootstocks and narrow leaves and spikes of pinkish-purple flowers occurring in great abundance in burned-over areas or recent clearings; an important honey

noun an American weedy plant with small white or greenish flowers

originFrom fire + weed. The fire-part may be of same origin as eld-part in dialectal Norwegian Nynorsk eldmerke (“fireweed”).

Etymology from Wiktionary, CC BY-SA 3.0