in botany, a genus of the monandria monogynia clasps. The interior part of the corolla is inflated and ringent; the inferior lip being trifid. There is but one species, viz. the arabicus, a native of both the Indies. The root of the costus is said to attenuate acid humours, and to promote expectoration, perspiration, and urine; but is now rarely to be met with in the shops.