The Collaborative International Dictionary of English v.0.48:

Monocotyledonae \Monocotyledonae\, Monocotyledones
\Monocotyledones\prop. n.
   A class of plants comprising seed plants that produce an
   embryo with a single cotyledon and parallel-veined leaves:
   grasses; lilies; palms; and orchids. It is divided into four
   subclasses or superorders: Alismatidae; Arecidae;
   Commelinidae; and Liliidae.

   Syn: class Monocotyledones, Monocotyledonae, class
        Monocotyledonae, Liliopsida, class Liliopsida.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Monocotyledonae
    n 1: comprising seed plants that produce an embryo with a single
         cotyledon and parallel-veined leaves: includes grasses and
         lilies and palms and orchids; divided into four subclasses
         or superorders: Alismatidae; Arecidae; Commelinidae; and
         Liliidae [syn: Monocotyledones, class Monocotyledones,
         Monocotyledonae, class Monocotyledonae, Liliopsida,
         class Liliopsida]