New World Encyclopedia defines a cassock as an outer robe that monks wear.
"Monk," New World Encyclopedia, accessed February 18, 2022
He is then given the outer cassock (Greek: Rasson, Exorasson, or Mandorrason; Slavonic: Riassa)—an outer robe with wide sleeves, something like the cowl used in the West, but without a hood—from which the name of Rassaphore is derived. He is also given a brimless hat with a veil, known as a klobuk, and a leather belt is fastened around his waist. His habit is usually black, signifying that he is now dead to the world, and he receives a new name. Although the Rassaphore does not make formal vows, he is still morally obligated to continue in the monastic estate for the rest of his life. Some will remain Rassaphores permanently without going on to the higher degrees.