This one has been asked for, so here goes…
To Jerry Thomas the word ‘fancy’ only apparently meant ‘fancy presentation’ – in this case, only by straining the drink into a previously lemon-accented goblet instead of serving it ‘on the rocks.’ Perhaps Thomas’ sense of ‘fancy’ was common at the time. If so, the meaning of ‘fancy’ would quickly come to mean less about presentation and more about constitution.
All of the above sources make their fancy drinks ‘fancy’ by both presentation and by adding fancy sweeteners. Traditionally speaking, a fancy sweetener is one that also supplies flavor beyond that of plain sugar. The fancy sweeteners in the above drinks include Curaçao liqueur and maraschino liqueur. Notice that, in contrast to Jerry Thomas in 1862, none of them use fancy sweeteners in the plain versions of their drinks.
Next, we will look at some pre-prohibition sources that make their fancy cocktails fancy only in essence, and not at all in presentation.
In the above recipes, it can be seen that the word fancy does not refer to fancy presentation at all. These drinks are fancy in constitution only, being at least partially-sweetened by fancy sweeteners. They are not garnished or presented any differently than the ‘plain’ cocktails. The authors of these recipes would probably have considered Jerry Thomas’ regular Brandy Cocktail of 1862 to be a fancy drink rather than a plain one.
Jerry Thomas is credited with authorship of the first American book dedicated to the art of mixing drinks. That certainly does not necessarily mean that his book is the best on the subject — or even that it was an accurate representation of the state of the art in his day. But, if taken as representative, it would seem that originally, a drink was considered ‘fancy’ in an American bar if it was fancy in image by being garnished or presented in a fancy way. It also seems that the word ‘fancy’ then matured into meaning that a drink was fancy in its essence, in addition to, or instead of, being fancy in its image.
Many other fancy cocktails became famous, even though not called fancy. The Manhattan Cocktail could be thought of as a fancy Whiskey Cocktail specifically made fancy by vermouth wine, which is sweet and adds other flavors. In fact, many true cocktails that have remained popular are fancy in their essence.