From Longman Dictionary of Contemporary Englishfrock coatˌfrock ˈcoat / $ ˈ../ noun [countable] DCCa knee-length coat for men, worn in the 19th century
Examples from the Corpus
frock coat• The more extreme designers have turned the jacket into a frock coat, emphasizing the Edwardian feel.• He was a cheery chap who wore a frock coat and a soiled black felt hat which had seen better days.• He, too, wore a black top hat, a black frock coat and black trousers.• Grant met them in a worn black frock coat and listened politely. 