delirious adj.

1590s, "a disordered state, more or less temporary, of the mind, often occurring during fever or illness," from Latin delirium "madness," from deliriare "be crazy, rave," literally "go off the furrow," a plowing metaphor, from phrase de lire, from de "off, away" (see de-) + lira "furrow, earth thrown up between two furrows," from PIE root *lois- "track, furrow." Meaning "violent excitement, mad rapture" is from 1640s.

Delirium tremens (1813) is medical Latin, literally "trembling delirium," introduced 1813 by British physician Thomas Sutton for "that form of delirium which is rendered worse by bleeding, but improved by opium. By Rayer and subsequent writers it has been almost exclusively applied to delirium resulting from the abuse of alcohol" ["The New Sydenham Society's Lexicon of Medicine and the Allied Sciences," London, 1882]. As synonyms, Farmer lists barrel-fever, gallon distemper, blue Johnnies, bottle ache, pink spiders, quart-mania, snakes in the boots, triangles, uglies, etc. 

word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."

Proto-Indo-European root meaning "furrow, track." 

It forms all or part of: delirious; delirium; last (n.1) "wooden model of a human foot used by shoemakers;" last (v.) "endure, go on existing;" learn; learning; Lehrjahre; lore.

It is the hypothetical source of/evidence for its existence is provided by: Latin lira "furrow;" Old Prussian lyso "field bed;" Old Church Slavonic lexa "field bed, furrow;" Old High German leisa "track," Gothic laistjan "to follow," Old English læran "to teach."