frock coat 
noun
A man’s double-breasted, long-skirted coat, now worn chiefly on formal occasions.On the left, under a tree, is the collector Victor Chocquet, in a dark frock coat, his overturned top hat on the ground behind him....
- Try any of those and you'll probably be stopped by a man in a frock coat wearing a gold-braided top hat.
- It was not until the turn of the last century that the suit established itself as standard daywear for the professional man, gradually supplanting the waisted frock coat and then the lounge coat.