The Collaborative International Dictionary of English v.0.48:

Hamamelidae \Hamamelidae\ n.
   a group of chiefly woody plants considered among the most
   primitive of angiosperms; they have a perianth poorly
   developed or lacking, and flowers often unisexual and often
   in catkins and often wind pollinated. The group contains 23
   families including the Betulaceae and Fagaceae (includes the
   Amentiferae); sometimes it is classified as a superorder.

   Syn: subclass Hamamelidae.
        [WordNet 1.5]

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):

Hamamelidae
    n 1: a group of chiefly woody plants considered among the most
         primitive of angiosperms; perianth poorly developed or
         lacking; flowers often unisexual and often in catkins and
         often wind pollinated; contains 23 families including the
         Betulaceae and Fagaceae (includes the Amentiferae);
         sometimes classified as a superorder [syn: Hamamelidae,
         subclass Hamamelidae]