differentia

n.	1.	(Logic) 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.
	2.	the set of characteristics distinguishing an entity from related entities.

Noun

1.

differentia - distinguishing characteristics (especially in different species of a genus)

difference