government vs system of rules

government and system of rules both are nouns.

Word	Noun	Adjective	Verb	Adverb
government	Yes	No	No	No
system of rules	Yes	No	No	No

As nouns, system of rules is a hypernym of government; that is, system of rules is a word with a broader meaning than government:

government: (government) the system or form by which a community or other political unit is governed
system of rules: a complex of methods or rules governing behavior

Other hypernyms of government include system.

government (noun)	system of rules (noun)
the act of governing; exercising authority	a complex of methods or rules governing behavior
(government) the system or form by which a community or other political unit is governed
the study of government of states and other political units
the organization that is the governing authority of a political unit