Maidenhair \Maid"en*hair`\, n. (Bot.) A fern of the genus {Adiantum} ({A. pedatum}), having very slender graceful stalks. It is common in the United States, and is sometimes used in medicine. The name is also applied to other species of the same genus, as to the Venus-hair. {Maiden grass}, the smaller quaking grass. {Maiden tree}. See {Ginkgo}.