"pyrethrum" in the noun sense

1. pyrethrum

made of dried flower heads of pyrethrum plants

2. pyrethrum, Dalmatian pyrethrum, Dalmatia pyrethrum, Tanacetum cinerariifolium, Chrysanthemum cinerariifolium

white-flowered pyrethrum of Balkan area whose pinnate leaves are white and silky-hairy below source of an insecticide sometimes placed in genus Chrysanthemum

3. painted daisy, pyrethrum, Tanacetum coccineum, Chrysanthemum coccineum

spring-flowering garden perennial of Asiatic origin having finely divided aromatic leaves and white to pink-purple flowers source of an insecticide sometimes placed in genus Chrysanthemum

4. Pyrethrum, genus Pyrethrum

used in former classifications for plants later placed in genus Chrysanthemum and now often included in genus Tanacetum

Source: WordNet® (An amazing lexical database of English)

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