ascendant vs ascendency

ascendant and ascendency both are nouns.

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

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

ascendant: position or state of being dominant or in control
ascendency: the state that exists when one person or group has power over another

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

ascendant (noun)	ascendency (noun)
someone from whom you are descended (but usually more remote than a grandparent)	the state that exists when one person or group has power over another
position or state of being dominant or in control

ascendant (adjective)	ascendency (adjective)
tending or directed upward
most powerful or important or influential