I've often wondered how two words so similar could be so opposite in meaning. A cortex, from the Latin word for bark (as in tree bark that is), is an outer layer, such the cortex of a kidney or better yet the outer layer of the brain containing the gray matter. A core on the other hand, is the middle or inner part (e.g. the molten core of the earth). M-W describes the etymology of core vaguely as "Middle English" but doesn't shed any real light on it. Can anybody explain?