Where does “pyrethrum” come from?

pyrethrum (Latin) comes from Ancient Greek πύρεθρον, from Ancient Greek πῦρ, from Proto-Indo-European péh₂wr̥ — bonfire; spelt.

Ancestry of “pyrethrum”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	πύρεθρον	pellitory of Spain
2	Ancient Greek	πῦρ	a fire; lightning; a fever
3	Proto-Indo-European	péh₂wr̥	bonfire; spelt