Part or all of this entry has been imported from the 1913 edition of Webster's Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing.
Origin of rochet
Middle English from Old French of Germanic origin
American Heritage Dictionary of the English Language, 5th Edition
The name rochettum is first traceable in England; in Germany and northern France the rochet was also called saroht (sarrotus) or sarcos (sarcotium).
The pope, John XXII., made him his principal chaplain, and presented him with a rochet in earnest of the first vacant bishopric in England.
This latter was reserved for the more important canons, and was worn over surplice or rochet in choir.
In the additional explanatory notes at the end of the book, after directions as to the wearing of surplice and hood in quire, in cathedral and collegiate churches (they are not made obligatory elsewhere), bishops are directed to wear, besides the rochet, a surplice or alb, and a cope or vestment, with a pastoral staff borne either by themselves or their chaplains.'
In the Roman Catholic Church the rochet is a tunic of white, and usually fine linen or muslin (battiste, mull) reaching about to the knee, and distinguished from the surplice by the fact that its arms are narrow and tight-fitting.