1550s, a classification in logic, from Latin species "kind, sort," originally "appearance, sight, a seeing," related to specere "to look at, to see, behold," from PIE *spek- (see scope (n.1)). Biological sense is from c.1600. Endangered species first attested 1964.
species spe·cies (spē'shēz, -sēz)
n. pl. species
A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding.
An organism belonging to such a category, represented in binomial nomenclature by an uncapitalized Latin adjective or noun following a capitalized genus name, as in the bacterium Escherichia coli.
A class of pharmaceutical preparations consisting of a mixture of dried plants in sufficiently fine division to be used in making boiled extracts or infusions.
A specific type of atomic nucleus, atom, ion, or molecule.
A group of organisms having many characteristics in common and ranking below a genus. Organisms that reproduce sexually and belong to the same species interbreed and produce fertile offspring. Species names are usually written lower case and in italics, as rex in Tyrannosaurus rex. See Table at taxonomy.
A group of closely related and interbreeding living things; the smallest standard unit of biological classification. Species can be divided into varieties, races, breeds, or subspecies. Red pines, sugar maples, cats, dogs, chimpanzees, and people are species; Siamese cats and beagles are varieties, not species. (See Linnean classification.)
Note: The term can be used to refer to any group of related things: “This species of novel has become quite popular in recent years.”