The formal or distinguishing part of the essence of a species, by which it is distinguished from other members of its genus; the characteristic attribute of a species; specific difference; as, a proper definition must have both genus and differentia.

the set of characteristics distinguishing an entity from related entities.

A universal idea or predicable which expresses a part of the essence of its subject, that part which distinguishes one species from another under the same genus.

distinguishing characteristics (especially in different species of a genus)

phrase used by Carl Linnaeus and other 'Aristotelian'; taxonomists which describes how a particular organism differs from other organisms in a genus.