reign vs govern

reign is a noun but govern is not a noun.

Word	Noun	Adjective	Verb	Adverb
reign	Yes	No	Yes	No
govern	No	No	Yes	No

As verbs, govern is a hypernym of reign; that is, govern is a word with a broader meaning than reign:

Other hypernyms of reign include rule.

reign (noun)	govern (noun)
royal authority; the dominion of a monarch
the period during which a monarch is sovereign
a period during which something or somebody is dominant or powerful

reign (verb)	govern (verb)
have sovereign power	exercise authority over; as of nations
be larger in number, quantity, power, status or importance	direct or strongly influence the behavior of
	bring into conformity with rules or principles or usage; impose regulations
	require to be in a certain grammatical case, voice, or mood