The Collaborative International Dictionary of English v.0.48:

Orchidaceous \Or`chi*da"ceous\, a. (Bot.)
   Pertaining to, or resembling, a natural order (Orchidaceae)
   of endogenous plants of which the genus Orchis is the type.
   They are mostly perennial herbs having the stamens and
   pistils united in a single column, and normally three petals
   and three sepals, all adherent to the ovary. The flowers are
   curiously shaped, often resembling insects, the odd or lower
   petal (called the lip) being unlike the others, and sometimes
   of a strange and unexpected appearance. About one hundred
   species occur in the United States, but several thousand in
   the tropics.
   [1913 Webster]

   Note: Over three hundred genera are recognized.
         [1913 Webster]