The Geneva gown is a full black robe with wide sleeves, and it is the academic dress of a university graduate rather than a vestment of any church. That is the whole point of it. The Reformed ministers of Geneva, Zurich and the cities that followed them held that the eucharist is not a sacrifice offered by a priest, and that the man in the pulpit stands there as a called and educated teacher of the word. Wearing the gown of a scholar rather than the alb and chasuble of a sacrificing priest states that position without a word being said.
It is commonly worn with preaching bands, two rectangles of white linen at the throat, which are likewise legal and academic in origin rather than ecclesiastical; the same bands are worn by advocates in several jurisdictions. An academic hood in the colours of the wearer's degree is often added, which underlines the same claim.
From Geneva it passed to the Reformed churches of France, the Netherlands, Scotland and Hungary, to English and American Presbyterians and Congregationalists, and to a great deal of Methodism, and it remains standard in many of those places. In much of the African American church tradition the gown carries a further set of associations, of learning and of dignity claimed in a society that withheld both, which is a history of its own rather than a footnote to the Genevan one.