genus

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Biology A taxonomic category ranking below a family and above a species and designating a group of species that are presumed to be closely related and usually exhibit similar characteristics. In a scientific name, the genus name is capitalized and italicized, for example,Ovis for sheep and related animals.
• noun Logic A class of objects divided into subordinate species having certain common attributes.
• noun A class, group, or kind with common attributes.

from The Century Dictionary.

• noun A kind; a sort; a class.
• noun In zoology and botany, a classificatory group ranking next above the species, containing a group of species (sometimes a single species) possessing certain structural characters different from those of any others. The value assigned to a genus is wholly arbitrary—that is, it is entirely a matter of opinion or current usage what characters shall be considered generic and thus constitute a genus; and genera are constantly modified and shifted by specialists, the tendency being mostly to restriction of genera, with the consequent multiplication of their number, and the coinage of new generic names. A genus has no natural, much less necessary, definition, its meaning being at best a matter of expert opinion; and the same is true of the species, family, order, class, etc. A genus of the animal kingdom in the time of Linnæus and other early naturalists was a group of species approximately equivalent to a modern family, sometimes even to an order. Probably upward of 100,000 generic names of as many supposed genera have been coined or used in zoölogy; those in current use at present are estimated at about 60,000, or an average of about (rather more than) one genus for every five species in the animal kingdom. In botany the genera are less restricted and average a much larger number of species, the 9,000 phanerogamic genera, for example, including 100,000 species. The tenable name of any genus is that which has priority of publication, if it has been properly published and characterized, and is not the same as the prior name of some other genus. The names of the genus and the species together form the scientific name of an animal or a plant. In writing the technical name of any animal or plant, the generic term always precedes the specific, and begins with a capital letter: as, Musca domestica, the house-fly, where Musca is the genus, and domestica differentiates the species. Genera are often subdivided into lesser groups called subgenera. (See subgenus.) A group of genera constitutes a family or subfamily. The name of a genus as such has properly no plural. If a genus name, as for example Ada, is pluralized, as Adœ, it means, not two or more genera named Ada, but either all the species of Ada, or some supergeneric group of which Ada is the type. The former usage is loose, or somewhat cant; the latter is frequent and regular in zoölogy. A genus name is always supposed to be Latin (though its derivation is in the great majority of cases from the Greek), and its plural, if used, is in Latin form; but when it is also Anglicized an English plural is used: as, the chinchillas, the animals of the genus Chinchilla.
• noun In old music, a formula or method of dividing the tetrachord. Three genera were distinguished: the diatonic, in which whole steps or “tones” were used; the chromatic, in which only half-steps or semitones were used; and the enharmonic, in which intervals less than a half-step were used.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.
• noun (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.
• noun (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.
• noun (Logic) the highest genus; a genus which can not be classed as a species, as being.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology, taxonomy a rank in the classification of organisms, below family and above species; a taxon at that rank
• noun A group with common attributes
• noun topology A number measuring some aspect of the complexity of any of various manifolds or graphs
• noun semantics Within a definition, a broader category of the defined concept.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a general kind of something
• noun (biology) taxonomic group containing one or more species