Hello,
I just want to add a little something so there is no confusion on using the term "fancy dress" in reference to historical dress/fashion/costume. Several folks here have commented that in the UK and Australia this term is applied to any costume party or Halloween type event, and that is something I was not aware of. That is good to know! However, the translation given above [ UK English to US English translation: fancy dress party = costume party] is not quite accurate, as in the USA, a Fancy Dress event was not the same thing as a costume party, and those terms are not interchangeable when referring to historical/vintage/antique fashion and dress. Here in the United Sates and in Canada (they had them in Europe too of course), a Fancy Dress Ball was very different from just a costume party, masquerade party or Halloween event. The term Fancy Dress meant a Fancy Dress Ball, and was a very lavish, well attended,carefully planned and orchestrated ball which had a definite theme to which the invited guests were required to follow. Almost always given by the very rich or the aristocracy, these opulent displays of wealth were often the best entertainment event of the "Season" for the upper classes, many of which became legendary. It was attended by powerful and important people and was carefully laid out, with grand music, dancing, champagne, and extravagant food. Guest often spent thousands of dollars (tens of thousands) on elaborate costumes of the finest silks, velvets, gilded threads, jewels, etc. Everyone at the ball wore a costume which was following the theme, often depicting a historical person, fictional character from literature or historical myth, or a certain era in history. If you find an antique garment which would be classed as Fancy Dress today, you are very lucky indeed.
I know that terms change meaning over time, and different countries use the terms differently, and not everyone is a stickler for accuracy when they deal in vintage clothing, so it is no biggie. But, I did want to share this bit of information so as not to have people start calling every Halloween or costume party garment a Fancy Dress costume.