Quiz: Remember the definition of mal de mer?
mid-14c., from Old French ierarchie, from Medieval Latin hierarchia "ranked division of angels" (in the system of Dionysius the Areopagite), from Greek hierarkhia "rule of a high priest," from hierarkhes "high priest, leader of sacred rites," from ta hiera "the sacred rites" (neuter plural of hieros "sacred;" see ire) + arkhein "to lead, rule" (see archon). Sense of "ranked organization of persons or things" first recorded 1610s, initially of clergy, sense probably influenced by higher. Related: Hierarchal; hierarchical.
An organisation with few things, or one thing, at the top and with several things below each other thing. An inverted tree structure. Examples in computing include a directory hierarchy where each directory may contain files or other directories; a hierarchical network (see hierarchical routing), a class hierarchy in object-oriented programming.