The Collaborative International Dictionary of English v.0.48:

Genera \Gen"e*ra\, n. pl.
   See Genus.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Genus \Ge"nus\ (j[=e]"n[u^]s), n.; pl. Genera. [L., birth,
   race, kind, sort; akin to Gr. ?. See Gender, and cf.
   Benign.]
   [1913 Webster]
   1. (Logic) A class of objects divided into several
      subordinate species; a class more extensive than a
      species; a precisely defined and exactly divided class;
      one of the five predicable conceptions, or sorts of terms.
      [1913 Webster]

   2. (Biol.) An assemblage of species, having so many
      fundamental points of structure in common, that in the
      judgment of competent scientists, they may receive a
      common substantive name. A genus is not necessarily the
      lowest definable group of species, for it may often be
      divided into several subgenera. In proportion as its
      definition is exact, it is natural genus; if its
      definition can not be made clear, it is more or less an
      artificial genus.
      [1913 Webster]

   Note: Thus in the animal kingdom the lion, leopard, tiger,
         cat, and panther are species of the Cat kind or genus,
         while in the vegetable kingdom all the species of oak
         form a single genus. Some genera are represented by a
         multitude of species, as Solanum (Nightshade) and Carex
         (Sedge), others by few, and some by only one known
         species.
         [1913 Webster]

   Subaltern genus (Logic), a genus which may be a species of
      a higher genus, as the genus denoted by quadruped, which
      is also a species of mammal.

   Summum genus [L.] (Logic), the highest genus; a genus which
      can not be classed as a species, as being.
      [1913 Webster]