Acorns are a distinctive nut that's often found on forest floors where oak trees grow. They are smooth and greenish, set in a rough brown base that's shaped like a little cup. The acorn is a seed, able to sprout roots if it falls in the right place, eventually growing into a new oak tree. Many animals eat acorns, some stockpiling the nuts for weeks. In Old English, æcern means "nut," from a Germanic origin.