Feather (pluma) you may know. Here our focus is on idioms (modismos) that use feather.
When a mortal asks you how you are, you could say “in fine feather” (de excelente humor). This is an idiom, that goes back many moons. When a farmer wanted to check the health of a chicken or turkey, he would review the feathers. If the feathers were shiny and flexible, it meant that the bird was in good health. So “fine feather” means in good health.
If someone does a very good job, a person might say that the excellent work is “a feather in his cap”. Perhaps in Spanish, you might say “es un tanto que se apunta”.
Sometimes you may pick up a big box and someone could ask you: is the box heavy? No, you reply, it is “as light as a feather” (tan ligero como una pluma). “Feather” is also a verb (emplumar), and sometimes people try “to feather their nest” (= hacer su agosto). This means that you make a lot of money, perhaps in an unfair or unreasonable way.