Cassock, long garment worn by Roman Catholic and other clergy both as ordinary dress and under liturgical garments. The cassock, with button closure, has long sleeves and fits the body closely. In the Roman Catholic church the colour and trim vary with the ecclesiastical rank of the wearer: the pope wears plain white, cardinals black with scarlet trim, archbishops and bishops black with red trim, and lesser clergy plain black. In choir and church ceremonies the pope wears a white silk cassock; cardinals wear scarlet, except in penitential Bordado artistico Polonia seasons when they wear purple; and lesser clergy wear plain black.
The cassock, though part of the canonical costume of the clergy, is not a liturgical vestment. It was originally the out-of-doors and domestic dress of European laity as well as clergy, and its survival among the latter when the secular fashions had changed is merely the outcome of ecclesiastical conservatism. In mild weather it was the outer garment; in cold weather it was worn under the tabard (a tunic with or without short sleeves) or chimere (a loose, sleeveless gown); sometimes in the Middle Ages the name chimere was given to it as well as to the sleeveless upper robe. In winter the cassock was often lined with furs varying in costliness with the rank of the wearer, and its colour also varied in the Middle Ages with ecclesiastical or academic status.