"A submission from France says the name Rhysand means "Perfection" and is of Welsh origin. According to a user from Georgia, U.S., the name Rhysand is of English origin and means "Bringer of dark power"."
I looked up the name meaning of Rhysand because in the ACOFAS interview, SJM says that she didn't even know what Rhys's name meant...
It literally means perfection and bringer of dark power XD