spe·cies (spēˈshēz, -sēz)

1. A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding.
2. 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.
3. 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.
4. A specific type of atomic nucleus, atom, ion, or molecule.