***], A hierarchy (Greek hieros sacred, arkho rule) is a system of ranking and organizing things. Different fields use the word in slightly different ways, but a particular definition, which the article will attempt first, captures the core of almost all uses. Originally, "hierarchy" meant "rule by priests". Since hierarchical churches such as the Roman Catholic and Eastern Orthodox churches had tables of organization that were "hierarchical" in the modern sense of the word, the term came to refer to more general organizational methods., [---