The word "understory" is a transparent compound formed from the native English prefix "under-" and the noun "story." Its logic is architectural and metaphorical, comparing the layered structure of a forest to the floors of a building. "Story," derived from Latin historia (narrative), evolved in Medieval Latin to denote a tier of windows with narrative images, which was then applied to a floor or level of a building. By combining "under" with this sense of "story," the term literally means "the lower level," aptly describing the plant life existing below the primary canopy layer in a wooded ecosystem.

Structure: under (beneath) + story (level) under: Old English. A preposition/adverb prefix meaning "beneath, below, lower in position." story: Latin (via Anglo-French). In this context, it means "a level or floor of a building," from Latin historia (narrative), but influenced by Medieval Latin historia used for a tier of painted windows or sculptures on a building, telling a story.