species

Species, speciei is feminine, fifth declension, from specio, "I look at". Like most fifth-declension nouns it is thin in the plural: species serves as nominative and accusative plural, and the genitive and dative plural are avoided in practice.

Two senses pull in opposite directions. First, the look of a thing, often a false look: "sub specie" plus a genitive is the standard phrase for a pretext, doing something under the appearance of something else. Second, the kind or class a thing belongs to, which is the logicians' use, subordinate to genus, and which the biologists took over wholesale in the eighteenth century. English species, specious, special and specimen all come from it, and specious kept the deceit.