Nature, in the broadest sense, is equivalent to the natural world, physical universe, material world or material universe. "Nature" refers to the phenomena of the physical world ...
http://en.wikipedia.org/wiki/Natural

adjective . 1. existing in or formed by nature (opposed to artificial): a natural bridge. 2. based on the state of things in nature; constituted by nature: Growth is a natural ...
http://dictionary.reference.com/search?q=natural

In science, the term natural science refers to a naturalistic approach to the study of the universe, which is understood as obeying rules or law of natural origin.
http://en.wikipedia.org/wiki/Natural_science

Medicine Man Natural (remedies have been used for centuries - and generations of healers can't be wrong. Can they?) by Edzard Ernst, July 13, 2004 The Guardian
http://www.skepdic.com/natural.html

The American Museum of Natural History is one of the world's preeminent institutions for scientific research and education, with collections of more than 32 million specimens and ...
http://www.amnh.org/