Arianell (ar-ee-ah-nell) is the name of a 6th century Welsh saint, a member of a royal family who became possessed by an evil spirit. Saint Dyfrig exorcised her and she then became a nun and followed him as a student. From the name Arianrhod of Welsh literature, meaning "silver, blessed," Arianell or Ariannell (formerly Arganhell) meaning "shining silver," is a little-used variant. Also connected to these two names is Arianwen, the daughter of a legendary 5th century Welsh chieftan, meaning "silver, blessed." A folk etymology of Arianrhod is "silver circle," referring to the moon. None of these were used on children until modern times. [source] Please note that the double L in Welsh has a unique sound, much like a hissing breath, or pronouncing "eth."
Add an A to the end to make Arianella, from Arianna and in turn from Ariadne, which is Greek, meaning "most holy." Ariadne was a character in Greek mythology who married Dionysus.