Definition of "definition"

What constitutes a good definition? In the era that modestly termed itself the "Enlightenment," some thinkers had the bright idea that the best definition of something was the shortest possible phrase that denoted that thing uniquely. This brilliant idea led to

man

1: featherless biped

whale

1: mammiferous animal without hind feet

In fact, the goodness of a definition depends on the context in which it is given: the previous knowledge that is assumed about the term being defined, the related terms from which it must be distinguished, the crucial qualities that need to be understood.