Full Idea
Goodness is a kind of completion: it is when something becomes as good as it may be that we say that it is complete, because that is when it pre-eminently conforms with its nature. A circle is complete when it is as good a circle as there could be.
Gist of Idea
Goodness is when a thing (such as a circle) is complete, and conforms with its nature
Source
Aristotle (Physics [c.337 BCE], 246a12)
Book Reference
Aristotle: 'Physics', ed/tr. Waterfield,Robin [OUP 1996], p.175
A Reaction
This, in turn, is said by Aristotle to result from the telos (purpose) of the thing. This won't eliminate the problem of relativism, unless we say that something cannot have an evil 'nature'. Was the Black Death good, by this definition?