hierarchy vs pecking order

hierarchy and pecking order both are nouns.

Word	Noun	Adjective	Verb	Adverb
hierarchy	Yes	No	No	No
pecking order	Yes	No	No	No

As nouns, hierarchy and pecking order are synonyms defined as:

hierarchy and pecking order: the organization of people at different ranks in an administrative body

Other synonyms of hierarchy include power structure.

hierarchy (noun)	pecking order (noun)
a series of ordered groupings of people or things within a system	the organization of people at different ranks in an administrative body
the organization of people at different ranks in an administrative body