An image returned by a surface, and a mind turning back on its own thinking. Both show you something you could not see directly.
Latin reflexio/reflectio (a bending back), from reflectere: re- (back) + flectere (to bend); reflection is what a surface or a mind does when it bends something back on itself rather than letting it pass straight through.
An image returned by a surface, and a mind turning back on its own thinking. Both show something the root already predicted: neither light nor thought can see itself directly, only bent back on itself.