Piccadilly is the place, Piccadilly is in Central London, and the name comes from a business based in pickadills or piccadills.
The place that now is Piccadilly circus, that used to be the road to Reading o the way to Colnbrook. in the 16th Century a gentleman called Robert Baker made a fortune selling pickadills, a piece of clothing to wear around the neck.
The name is supposed to come from the Spanish word picadillo or picadura. Never the less the tailor made his good fortune due to this garment and it is believed that the name stick to the area until this days.
There are several theories about the name of pickadill or piccadill one is that is a welsh word used as a reference of the shape of the garment. Another is that it has the Spanish origin as both words sound quite similar.
Luckily the use of the garment in question is in no use anymore, but the use of the name for the area that used to sell has remain.
On this day and age that clothing style is gone. But the stylish tailors are still in 2019 around in the area Jermin street. It has a nice range of shirt shops. Plus quite a few independent retailers that have been for generations in the area.