What does the Greek term "physis" mean?

Physis (Greek: φύσις PHEE-sys) is a Greek theological, philosophical, and scientific term usually translated into English as "nature".

The term is central to Greek philosophy, and as a consequence to Western philosophy as a whole. In pre-Socratic usage, physis was contrasted with νόμος, nomos, "law, human convention." Since Aristotle, however, the physical (the subject matter of physics, properly τὰ φυσικά "natural things") has more typically been juxtaposed to the metaphysical.

Theologians of the early Christian period differed in the usage of this term. In Antiochene circles, it connoted the humanity or divinity of Christ conceived as a concrete set of characteristics or attributes. In Alexandrine thinking, it meant a concrete individual or independent existent and approximated to hypostasis without being a synonym. While it refers to much the same thing as ousia it is more empirical and descriptive focussing on function while ousia is metaphysical and focuses more on reality.

The Greek adjective phusikos is represented in various forms in modern English: As physics "the study of nature", as physical (via Middle Latin physicalis) referring both to physics (the study of nature, the material universe) and to the human body. In medicine the suffix -physis occurs in such compounds as symphysis, epiphysis, and a few others, in the sense of "a growth". The physis also refers to the "growth plate", or site of growth at the end of long bones.