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.
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.
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
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
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.