tyranny vs ascendency

tyranny and ascendency both are nouns.

Word	Noun	Adjective	Verb	Adverb
tyranny	Yes	No	No	No
ascendency	Yes	No	No	No

As nouns, ascendency is a hypernym of tyranny; that is, ascendency is a word with a broader meaning than tyranny:

tyranny: dominance through threat of punishment and violence
ascendency: the state that exists when one person or group has power over another

Other hypernyms of tyranny include ascendance, ascendancy, ascendence, control, dominance.

tyranny (noun)	ascendency (noun)
a form of government in which the ruler is an absolute dictator (not restricted by a constitution or laws or opposition etc.)	the state that exists when one person or group has power over another
dominance through threat of punishment and violence