excellence vs excellency

excellence and excellency both are nouns.

Word	Noun	Adjective	Verb	Adverb
excellence	Yes	No	No	No
excellency	Yes	No	No	No

As nouns, excellence and excellency are synonyms defined as:

excellence and excellency: an outstanding feature; something in which something or someone excels

excellence (noun)	excellency (noun)
the quality of excelling; possessing good qualities in high degree	an outstanding feature; something in which something or someone excels
an outstanding feature; something in which something or someone excels