With all the hats this season, it is important to know your facts.
Here is a trilby:
The name of the hat comes from George du Maurier's 1894 novel, Trilby. There was a London stage play made of the novel, and one character wore a hat like a fedora, but with a narrower brim. It was dubbed a trilby.
Here is a fedora:
As you can see, the brim is larger, giving the fedora a hint more dramatic flair. Fedoras were also named for a London stage play. The title character in Princess Fedora by Victorien Sardou in 1891 wore such a hat.
Here is an alpaca:
Alpacas look kind of like llamas. They eat hay and grass.
Here, you can get an alpaca fedora, and totally baffle your friends with linguistic glee:
So now, you know.