Cassock
The cassock is a vestment worn by clergy, and by laity in choir dress. It is common for clergy to wear simply their cassock during secular life as a mark of their office. Cassocks are usually modest black coats, fastened by buttons from the neck down to the waist, but can sometimes come in different colors.
Etymology
The term cassock is derived from the Middle French casaque, meaning a long coat.
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Description
Some cassocks are single breasted (having only one column of buttons) while others are double breasted (being buttoned in two columns). It is usually long enough to fall just about the feet of the wearer, with long sleeves as well. Often clergy will wear cassocks along with preaching bands or a clerical collar.
Use in Anglicanism
Wearing a single breasted cassock is associated with Anglo-Catholicism, while a double breasted cassock is associated with the more Protestant wing of Anglicanism.
Traditionally single breasted cassocks in Anglicanism had thirty-nine buttons symbolizing both the Thirty-Nine Articles of Religion but also St. Paul’s “Forty stripes save one” recorded in 2 Cor. 11.
Some Anglo-Catholics would reportedly leave one button unbuttoned for every article of the Thirty-Nine Articles to which they objected to.