High Quality Content by WIKIPEDIA articles! Chreod, is a portmanteau term coined by 20th century biologist Conrad Hal Waddington that combines the Greek word for "determined" or "necessary" and the word for "pathway." The term was used along with homeorhesis, which describes a system that returns to a steady trajectory in contrast to homeostasis which describes a system which returns to a steady state. Architectural Theorist Sanford Kwinter described the concept of the cherod as "the most important concept of the 20th century."