The Collaborative International Dictionary of English v.0.48:

Twyblade \Twy"blade`\, n.
   See Twayblade.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Twayblade \Tway"blade`\, n. (Bot.)
   Any one of several orchidaceous plants which have only two
   leaves, as the species of Listera and of Liparis.
   [Written also twyblade.]
   [1913 Webster]