The Collaborative International Dictionary of English v.0.48:

Dicotyledonae \Dicotyledonae\ n. (Bot.)
   a class of plants comprising those seed plants that produce
   an embryo with two cotyledons and net-veined leaves; divided
   into six (not always well distinguished) subclasses (or
   superorders): Magnoliidae and Hamamelidae (considered
   primitive); Caryophyllidae (an early and distinctive
   offshoot); and three more or less advanced groups:
   Dilleniidae; Rosidae; Asteridae.

   Syn: Dicotyledones, class Dicotyledones, class Dicotyledonae,
        Magnoliopsida, class Magnoliopsida.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Dicotyledonae
    n 1: comprising seed plants that produce an embryo with paired
         cotyledons and net-veined leaves; divided into six (not
         always well distinguished) subclasses (or superorders):
         Magnoliidae and Hamamelidae (considered primitive);
         Caryophyllidae (an early and distinctive offshoot); and
         three more or less advanced groups: Dilleniidae; Rosidae;
         Asteridae [syn: Dicotyledones, class Dicotyledones,
         Dicotyledonae, class Dicotyledonae, Magnoliopsida,
         class Magnoliopsida]