permethrin noun1 •A synthetic insecticide, C₂₁H₂₀Cl₂O₃, used to treat head lice, nits, and scabies; as an active ingredient in flea collars; and to eradicate woodworm infestations.*Permethrin is the artificial version of pyrethrin, which is made from chrysanthemum flowers. — 2023 formspermethrins
