Cassock

The cassock, or soutane, is an item of Christian clerical clothing used by the clergy of Catholic, Eastern Orthodox, Anglican and Reformed churches, among others. "Ankle-length garment" is the literal meaning of the corresponding Latin term, vestis talaris. It is related to habit traditionally worn by nuns, monks, and friars.

The cassock derives historically from the tunic that in ancient Rome was worn underneath the toga and the chiton that was worn beneath the himation in ancient Greece. In religious services, it has traditionally been worn underneath vestments, such as the alb.

In the West, the cassock is little used today except for religious services; but in many countries it was the normal everyday wear of the clergy until the second half of the 20th century, when it was replaced even in those countries by a conventional suit, distinguished from lay dress by being generally black and by incorporating a clerical collar.

The word "cassock" comes from Middle French casaque, meaning a long coat. In turn, the old French word may come ultimately from Turkish "quzzak" (nomad, adventurer – the source of the word "Cossack"), an allusion to their typical riding coat, or from Persian کژاغند "kazhāgand" (padded garment) – کژ "kazh" (raw silk) + آغند "āgand" (stuffed). The name was originally specially applied to the dress worn by soldiers and horsemen, and later to the long garment worn in civil life by both men and women. As an ecclesiastical term the word "cassock" came into use somewhat late (as a translation of the old names of subtanea, vestis talaris, toga talaris, or tunica talaris), being mentioned in canon 74 of 1604; and it is in this sense alone that it now survives.

...
Wikipedia