in reference to forest vegetation, also under-story, 1902, from under + story (n.).
Entries linking to understory
under prep., adv.
Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (source also of Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (source also of Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").
Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).
Under the weather "indisposed" is from 1810. Under the table is from 1913 in the sense of "very drunk," 1940s in sense of "illegal" (under-board "dishonest" is from c. 1600). To keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832.
story n.1
"connected account or narration of some happening," c. 1200, originally "narrative of important events or celebrated persons of the past," from Old French estorie, estoire "story, chronicle, history," from Late Latin storia, shortened from Latin historia "history, account, tale, story" (see history).
A story is by derivation a short history, and by development a narrative designed to interest and please. [Century Dictionary]
Meaning "recital of true events" first recorded late 14c.; sense of "narrative of fictitious events meant to entertain" is from c. 1500. Not differentiated from history until 1500s. For the sense evolution compare Gaelic seanachas "history, antiquity," also "story, tale, narration," from sean "old, ancient" + cuis "a matter, affair, circumstance."
As a euphemism for "a lie" it dates from 1690s. Meaning "newspaper article" is from 1892. Story-line first attested 1941. That's another story "that requires different treatment" is attested from 1818. Story of my life "sad truth" first recorded 1938, from typical title of an autobiography.