sonder (n.) the realization that each passerby has a life as vivid and complex as your own. The Dictionary of Obscure Sorrows is "a compendium of invented words" written by graphic designer and editor John Koenig.
It comes from the Greek word εὔνοια, meaning "well mind" or "beautiful thinking. Eunoia is the shortest English word containing all five main vowel graphemes. In book eight of Nicomachean Ethics, Aristotle uses the term to refer to the kind and benevolent feelings of goodwill a spouse has which form the basis for the ethical foundation of human life.