The Collaborative International Dictionary of English v.0.48:

maidenhair \maid"en*hair`\, maidenhair fern \maidenhair fern\,
   n. (Bot.)
   Any of various small to large terrestrial ferns of the genus
   Adiantum having very slender graceful stalks and delicate
   palmately branched fronds, especially (Adiantum pedatum).
   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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

maidenhair
    n 1: any of various small to large terrestrial ferns of the
         genus Adiantum having delicate palmately branched fronds
         [syn: maidenhair, maidenhair fern]