The Collaborative International Dictionary of English v.0.48:

lady-slipper \lady-slipper\ n. (l[=a]"d[y^] sl[i^]p"p[~e]r),
   (Bot.)
   Same as lady's slipper.

   Syn: lady's slipper, lady's-slipper, slipper orchid.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

lady-slipper
    n 1: any of several chiefly American wildflowers having an
         inflated pouchlike lip; difficult or impossible to
         cultivate in the garden [syn: lady's slipper, lady-
         slipper, ladies' slipper, slipper orchid]