Medical Definition of arnica
1a capitalized : a large genus of herbs (family Compositae) having flower heads that are discoid or have bright yellow raysb: a plant of the genus Arnica
2a: the dried flower head of any of several herbs of the genus Arnica (especially A. montana) used for stimulant and local irritant effect especially in the form of a liniment for bruises, sprains, and swellingsb: a tincture made from arnica
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