This article discusses the lounge suit (including business suits), elements of informal dress code.
All the other official guests without exception had worn lounge suits.
The frock coat was widely worn in much the same situations as modern lounge suits and formalwear, with different variations.
Because black was then reserved for formalwear, it was unknown as a colour for lounge suits, so the term was unambiguous.
For example, black tie (originally "dinner clothes") was initially described as informal, while the lounge suit, now standard business attire, was originally considered (as its name suggests) casual wear.
Since the 1950s it has been used as a black version of the lounge suit as an informal look to the dinner jacket.
However, the lounge suit was not considered appropriate for public settings until the 1870s.
This article discusses the history of the lounge suit, often called a business suit when made in dark colours and of conservative cut.
