An acorn is the nut that grows on an oak tree. It sits in a little rough cup, then falls in autumn. Squirrels bury them; some of those buried nuts grow into new oaks. You cannot treat it like a snack from the shop — raw acorns taste bitter and can upset the stomach unless they are prepared in a special way, which most people never do. Children often learn the word early because the shape is easy to draw and the oak is a famous tree. Though actually, the English spelling looks like a neat little story (oak + corn), and that look has fooled people for a long time. The meaning is still just “the oak’s nut.”