Nature: In the broadest terms, the totality of what exists at all levels in the universe.
In its narrower signification, nature refers to the non-humanly constructed environment of life and life-support systems.
In the history of speculative metaphysics, nature also refers to the essence of things, or that defining feature which distinguishes kinds of things from other kinds of things.
Source: ‘What is Good? What is Bad? The Value of All Values across Time, Place and Theories’ by John McMurtry, Philosophy and World Problems, Volume I-III, UNESCO in partnership with Encyclopedia of Life Support Systems: Oxford, 2004-11.