cassock [M16th] This clerical garment has a disreputable history. It comes via French casaque ‘long coat’, from Italian casacca ‘riding coat’, probably based on Turkic kazak ‘vagabond, nomad’, source also of Cossack [L16th]. A cassock once referred to a long coat worn by some soldiers in the 16th and 17th centuries; the ecclesiastical use appears to have arisen in English in the 17th century.