persistency vs persistence

persistency and persistence both are nouns.

Word	Noun	Adjective	Verb	Adverb
persistency	Yes	No	No	No
persistence	Yes	No	No	No

As nouns, persistency and persistence are synonyms defined as:

Other synonyms of persistency include doggedness, perseverance, pertinacity, tenaciousness, tenacity.

persistency (noun)	persistence (noun)
persistent determination	the act of persisting or persevering; continuing or repeating behavior
	persistent determination
	the property of a continuous and connected period of time