Physis (φύσις) is a Greek theological, philosophical, and scientific term usually translated into English as "nature". In the Odyssey, Homer uses the word once (its earliest known occurrence), referring to the intrinsic way of growth of a particular species of plant. In other very early uses it had such a meaning: related to the natural growing of plants, animals, and other features of the world as they tend to develop without external influence. But in the pre-Socratic philosophers it developed a complex of other meanings.
Since Aristotle, the physical (the subject matter of physics, properly τὰ φυσικά "natural things") has often been contrasted with metaphysical (the subject of metaphysics), discussed in Aristotle's works so titled, Physics and Metaphysics.
"Physis" was understood by Thoreau as coming from darkness into light, biologically, cosmically, cognitively. (Walden Pond, 'Spring')
Leo Strauss felt this was a sign of something new in the world which the Greeks discovered – something distinct from the concept of a "way" general to other cultures. (See also dharma and tao, for the development of related notions in other cultures.)
In medicine the element -physis occurs in such compounds as symphysis, epiphysis, and a few others, in the sense of a growing. The physis also refers to the "growth plate," or site of growth at the end of long bones.
Phusis was an Ancient Greek word often translated as birth or nature. The term represents a slightly different transcription from the term physis. Martin Heidegger a German phenomenologist and proto-existentialist, made the argument in An Introduction to Metaphysics that this translation of phusis, is an oversimplication and narrowing of the original dynamism of the term that harms our understanding of early Greek philosophy. Heidegger translated phusis as the 'emerging-abiding-sway,' arguing that it provided a more complex and accurate understanding of existence than the earlier translation. The problem, for Heidegger, is that translators view this Greek term (among others) through the lenses provided by later philosophy. Implicit in such a perspective is the belief that modern thinkers are more advanced than earlier thinkers. For Heidegger, early Greek philosophy authentically captured the dynamism of Being, an understanding that became ossified through the layers of metaphysical systematization that was imposed upon it with the passing of time.