We don't have synonyms for cassiel yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are cassie, cassel and castiel.
(n) :
An angel appearing in extracanonical Jewish, Christian, and Islamic mystical and magical works, often as one of the Seven Archangels, the angel of Saturn, and in other roles.
(n) :
An angel appearing in extracanonical Jewish, Christian, and Islamic mystical and magical works, often as one of the Seven Archangels, the angel of Saturn, and in other roles.