One way to hold feeder in your head: it is the thing standing in the middle of a supply. On one side there is a store of something — seeds, paper, water, electricity, passengers. On the other side there is someone or something that needs it. The feeder is what keeps passing it across, a little at a time, so the far side never runs dry. A bird feeder passes out seeds all day while you are at work; a paper feeder passes sheets into a printer; a small river passes water into a big one. Because the English verb feed points both ways — you feed a child, and cattle feed on grass — the same word can now and then name the eating end instead.