Cassock

From Middle French casaque ("cloak").

(plural cassocks)

(obsolete) A military cloak or long coat worn by soldiers or horsemen in the 16th and 17th centuries. 16th-17th c.
(obsolete) A coarse, loose cloak or gown, worn by women, sailors, shepherds, countryfolk etc. 16th-17th c.
An item of clerical clothing: a long, sheath-like, close-fitting, ankle-length robe worn by clergy members of some Christian denominations. from 17th c.

1918, W. B. Maxwell, The Mirror and the Lamp Chapter 10, It was a joy to snatch some brief respite, and find himself in the rectory drawingâ€“room. Listening here was as pleasant as talking; just to watch was pleasant. The young priests who lived here wore cassocks and birettas; their faces were fine and mild, yet really strong, like the rector's face; and in their intercourse with him and his wife they seemed to be brothers.
1956, w, Crime out of Mind Chapter 13, In one of the aisles there was an elaborately carved confessional box and I recognised the village priest in his heavy mountain boots and black cassock as he entered it and drew the dark velvet curtains behind him.