Real Dictionary

hierarchy
a number of things growing, fastened, or occurring close together [...]
a system of persons or things arranged in a graded order [...]
the division of a physical or abstract whole into its constituent parts to examine or determine their relationship or value [...]
The hierarchy of an organization such as the Church is the group of people who manage and control it.
countable noun: A hierarchy of ideas and beliefs involves organizing them into a system or structure.
variable noun: A hierarchy is a system of organizing people into different ranks or levels of importance, for example in society or in a company.

hierarchy in American English
a system of church government by priests or other clergy in graded ranks
noun: any system of persons or things ranked one above another

hierarchy in British English
noun: a system of persons or things arranged in a graded order