Online Etymology Dictionary

hypo-: word-forming element meaning "under, beneath; less, less than" (in chemistry, indicating a lesser oxidation), from Greek hypo (prep. and adverb) "under, beneath; up from under; toward and under (i.e. into)," from PIE *upo "under; up from under; over" (see sub-).
hypo-allergenic (adj.): also hypoallergenic, 1950; see hypo- + allergen + -ic.
hypocaust (n.): "arched fire chamber for heating rooms above via pipes," 1670s, from Late Latin hypocaustum, from Greek hypokauston, literally "heated from below," from hypo- "under; up from under" (see hypo-) + kauston, verbal adjective of kaiein "to burn" (see caustic).
hypochondria (n.): "unfounded belief that one is sick," by 1816; a narrowing from the earlier sense "depression or melancholy without real cause" (1660s); from Middle English medical term ipocondrie "lateral regions of the upper abdomen" (late 14c.). This is from Late Latin hypochondria, from Greek hypokhondria (neuter plural of hypokhondrios), from hypo- "under" (see hypo-) + khondros "cartilage" (in this case, of the false ribs); see chondro-.

The sense "morbid melancholy" reflects the ancient belief that the viscera of the hypochondria (liver, gall bladder, spleen) were the seat of melancholy and the source of the vapors that caused such feelings. The attempt to put it on a scientific bases passes through hypochondriasis. Also see hype (n.). The poet Cowper is an oft-cited example in late 18c. literature. The focus of sense on the particular symptom "unfounded belief that one is sick" seems to begin 1790s with William Cullen, M.D., professor of physic in the University of Edinburgh, who made a specialty of the topic:
A languor, listlessness, or want of resolution and activity, with respect to all undertakings; a disposition to seriousness, sadness, and timidity; as to all future events, an apprehension of the worst or most unhappy state of them; and, therefore, often upon slight grounds an apprehension of great evil. Such persons are particularly attentive to the state of their own health, to every the smallest change of feeling in their bodies; and from any unusual sensation, perhaps of the slightest kind, they apprehend great danger, and even death itself. In respect to these feelings and fears, there is commonly the most obstinate belief and persuasion. [Cullen, "First Lines of the Practice of Physic," Edinburgh, 1791]
Though to Cullen the clinical definition of hypochondria also included physical symptoms and pains as well as these mental delusions. As the old medical beliefs faded, the word dropped from clinical use but remained in popular use for "groundless morbid fear for one's health." In the 1830s hypochondria could mean merely "morbid melancholy," also "apprehension of evil respecting health, without sufficient cause," and "upper abdomen."
hypochondriac (adj.): 1590s, "pertaining to the hypochondria," also "afflicted with melancholy," from French hypocondriaque (16c.), from Medieval Latin hypochondriacus, from Greek hypokhondriakos "pertaining to the upper abdomen, affected in the hypochondrium," from hypokhondria (see hypochondria). The noun is from 1630s as "melancholy person;" in the modern sense from 1866.
hypochondriasis (n.): disease evidenced by lowness of spirits, sluggishness, indolence, loss of interest in amusements, a wish to be alone, etc., 1765, from hypochondria in its older sense of "melancholy without cause," treated here as a disorder of the body and given the medical ending -osis to denote "a state of disease." The definitions of hypochondria then expanded to include this sense and that has become the usual word for it.
To call the Hypochondriaſis a fanciful malady, is ignorant and cruel. It is a real, and a ſad diſeaſe : an obſtruction of the ſpleen by thickened and diſtempered blood ; extending itſelf often to the liver, and other parts ; and unhappily is in England very frequent : phyſick ſcarce knows one more fertile in ill ; or more difficult of cure. [J. Hill, M.D., "Hypochondriasis," London, 1766]
hypocoristic (adj.): "forming a diminutive of endearment," 1851, from Greek hypo- "under, beneath, less than."
hypocrisy (n.): c. 1200, ipocrisie, "the sin of pretending to virtue or goodness," from Old French ypocrisie, from Late Latin hypocrisis "hypocrisy," also "an imitation of a person's speech and gestures," from Attic Greek hypokrisis "acting on the stage; pretense," metaphorically, "hypocrisy," from hypokrinesthai "play a part, pretend," also "answer," from hypo- "under" (see hypo-) + middle voice of krinein "to sift, decide" (see crisis). The sense evolution in Attic Greek is from "separate gradually" to "answer" to "answer a fellow actor on stage" to "play a part." The h- was restored in English 16c.
Hypocrisy is the art of affecting qualities for the purpose of pretending to an undeserved virtue. Because individuals and institutions and societies most often live down to the suspicions about them, hypocrisy and its accompanying equivocations underpin the conduct of life. Imagine how frightful truth unvarnished would be. [Benjamin F. Martin, "France in 1938," 2005]
hypocrite (n.): c. 1200, ypocrite, "false pretender to virtue or religion," from Old French ypocrite (12c., Modern French hypocrite), from Church Latin hypocrita "a hypocrite," from Greek hypokrites "stage actor; pretender, dissembler," from hypokrinesthai (see hypocrisy).
hypocritic (adj.): 1530s, from Greek hypokritikos "acting a part, pretending" (see hypocrisy). Hypocritical is the more common form.
hypocritical (adj.): 1540s (implied in hypocritically), from hypocritic, which was used in the same sense, + -al (1). It won out over hypocritish (1520s), hypocritic (1530s). Middle English used simple hypocrite as the adjective (c. 1400) as well as the noun.
hypodermic (adj.): 1830, from hypo- "under" + derma "skin" + -ic. Hypoderma is attested from 1826 as "tissue just beneath the skin."
hypogamy (n.): "marriage of a woman into a lower class, caste, or tribe," 1940, an anthropologist's word first used in an Indian context, from hypo- "under, beneath" + -gamy "marriage." Related: Hypogamous.
hypogastrium (n.): "lower belly," 1680s, from Modern Latin hypogastrium, from Greek hypogastrion, from hypo "under, below" (see hypo-) + gaster (genitive gastros) "belly, paunch; womb" (see gastric). Related: Hypogastric (1650s).
hypogean (adj.): "living below the ground," 1803, from Greek hypogeios "underground," from hypo "under" (see hypo-) + ge "earth" (see Gaia). Opposed to epigean.
hypoglycemia (n.): 1893, from Latinized form of Greek elements hypo- "under" (see hypo-) + glykys "sweet" (see glucose) + haima "blood" (see -emia).
hypomania (n.): "manic elation accompanied by quickened perception," 1843 (as a clinical word from 1882, from German hypomanie, 1881); see hypo- "under, beneath" + mania. Related: Hypomaniac; hypomanic.
hyponymy (n.): 1955, a linguist's word, from hypo- + second element from Greek onyma "name" (see name (n.)), with abstract noun ending. The relationship between two words where one may invariably be replaced by the other without changing the sense but not vice versa.
hypostasis (n.): Greek word meaning "substance; subsistence;" from hypo "under, beneath" (see hypo-) + stasis "a standing, a position" (see stasis). Used in Ecclesiastical Greek since earliest times for "person" of God in the Trinity. This led to centuries of wrangling over the definition. "In the necessity they were under of expressing themselves strongly against the Sabellians, the Greeks made choice of the word hypostasis, and the Latins of persona ; which change proved the occasion of endless disagreement" ["Pantologia, A New Cabinet Cyclopaedia," London, 1819]. The same word in old medicine meant "sediment in the urine."
hypotaxis (n.): 1844, earlier in German; see hypo- + taxis.
hypotenuse (n.): the side of a right triangle that is opposite the right angle, 1570s, from Late Latin hypotenusa, from Greek hypoteinousa "stretching under" (the right angle), fem. present participle of hypoteinein, from hypo- "under" (see hypo-) + teinein "to stretch" (see tenet). Formerly often erroneously hypothenuse. Related: Hypotenusal.
hypothalamus (n.): 1896, coined 1893 in German from Greek hypo- "under" (see sub-) + thalamus "part of the brain where a nerve emerges." So called for its position below and in front of the thalamus.
hypothecate (v.): 1680s, "pledge (something) without giving up control of it; pawn; mortgage," from hypothecat-, past participle stem of Medieval Latin hypothecare, from Late Latin hypotheca "a pledge," from Greek hypotheke "a deposit, pledge, mortgage," from hypo- "beneath, under" (see hypo-) + tithenai "to put, place" (see theme). Related: Hypothecated; hypothecating; hypothecation; hypothecary.
hypothermia (n.): 1877, Modern Latin, from hypo- "under" (see hypo-) + Greek therme "heat" (see thermal) + abstract noun ending -ia.
hypotheses (n.): plural of hypothesis.
hypothesis (n.): 1590s, "a particular statement;" 1650s, "a proposition, assumed and taken for granted, used as a premise," from Middle French hypothese and directly from Late Latin hypothesis, from Greek hypothesis "base, groundwork, foundation," hence in extended use "basis of an argument, supposition," literally "a placing under," from hypo- "under" (see hypo-) + thesis "a placing, proposition" (see thesis). A term in logic; narrower scientific sense is from 1640s.
hypothesise (v.): chiefly British English spelling of hypothesize; for suffix, see -ize. Related: Hypothesised; hypothesising.
hypothesize (v.): 1738, from hypothesis + -ize. Related: Hypothesized; hypothesizing.
hypothetical (adj.): 1580s, from Latinized form of Greek hypothetikos "pertaining to a hypothesis," from hypothesis (see hypothesis). Hypothetic (1670s) is less common. Related: Hypothetically.
hypotonia (n.): 1876, medical Latin, from hypo- + Greek tonos "tone" (see tenet) + abstract noun ending -ia.
hypotonic (adj.): "having reduced tension or pressure," 1873, from hypo- + tonic.
hypoxia (n.): 1941, from hypo- + oxygen + abstract noun ending -ia. Related: Hypoxic.
hypsi-: word-forming element meaning "high, on high, lofty," from Greek hypsi (adv.) "aloft, on high," related to hypsos "height" (see hypso-).
hypso-: word-forming element meaning "height," from Greek hypsos "height, top," from PIE *upso-, from root *upo "under, up from under, over" (see sub-). The Greek word is cognate with Sanskrit os "above, over," Old Church Slavonic vysoku "high."
hypsography (n.): "the study of comparative altitudes," 1885; see hypso- + -graphy. Related: Hypsographic (1848), of contour maps; earlier in French and German.
hypsometry (n.): "the measuring of altitudes," 1560s; see hypso- + -metry.
Hyrcania: ancient region southeast of the Caspian Sea, from Greek Hyrkania, said to be from an Indo-European *verkana "country of wolves" [Zonn, I., et al., "The Caspian Sea Encyclopedia," 2010]. "Hyrcania was the wild region par excellence to the ancients" [OED]. Related: Hyrcanian.
hyssop (n.): Old English ysope, from Irish Latin hysopus (Medieval Latin ysopus), from Greek hyssopos, a plant of Palestine, used in Jewish purification rites, from Hebrew 'ezobh (compare Syriac zupha, Arabic zufa). Since Old English the word has been used both of a small, bushy, aromatic herb native to southern Europe and the Biblical hyssop, a different plant, used in purification rituals, variously identified.
hysterectomy (n.): "surgical excision of the uterus," 1881, coined in English from Greek hystera "womb" (see uterus) + -ectomy.
hysteresis (n.): "a lagging of one of two related phenomenon behind the other" [Century Dictionary], 1881, from Greek hysteresis "a coming short, a deficiency," from hysteros "later, second, after," from PIE *ud-tero-, from root *ud- "up, out" (see out (adv.)). Earlier as a term in rhetoric.
hysteria (n.): nervous disease, 1801, coined in medical Latin as an abstract noun from Greek hystera "womb," from PIE *udtero-, variant of *udero- "abdomen, womb, stomach" (see uterus). Originally defined as a neurotic condition peculiar to women and thought to be caused by a dysfunction of the uterus. With abstract noun ending -ia. General sense of "unhealthy emotion or excitement" is by 1839.
hysteric (adj.): 1650s, "hysterical; relating to or affected with hysteria; emotionally disordered and frantic," from Latin hystericus, from Greek hysterikos "belonging to the womb" (see hysterical, which is the more common adjective). As a noun, "one who is hysterical," from 1751.
hysterical (adj.): 1610s, "characteristic of hysteria," from Latin hystericus "of the womb," from Greek hysterikos "of the womb, suffering in the womb," from hystera "womb" (see hysteria). Meaning "very funny" (by 1939) is from the notion of uncontrollable fits of laughter. For "inclined to hysteria," American English formerly had the colloquial hystericky (1792). Related: Hysterically.
hysterics (n.): "fits or convulsions of hysteria," 1727, from hysterical. Sometimes in 19c. jocularly folk-etymologized as high-strikes (1838).
hysteron-proteron (n.): 1560s, from Late Latin, from Greek hysteron-proteron, literally "the latter (put as) the former." A cart-before-the-horse figure of speech, in which what should come last is put first. From hysteron, neuter of hysteros "latter, second, after" (from PIE *ud-tero-, from root *ud- "up, out;" see out (adv.)) + proteron, neuter of proteros "before, former," from PIE *pro-, from root *per- (1) "forward, through" (see per).