hydrogen (n.) Look up hydrogen at Dictionary.com
colorless, gaseous element, 1791, hydrogene, from French hydrogène (Modern Latin hydrogenium), coined 1787 by G. de Morveau, Lavoisier, Berthollet, and Fourcroy from Greek hydr-, stem of hydor "water" (see water (n.1)) + French -gène "producing" (see -gen). So called because it forms water when exposed to oxygen. Nativized in Russian as vodorod; in German, it is wasserstoff, "water-stuff." An earlier name for it in English was Cavendish's inflammable air (1767). Hydrogen bomb first recorded 1947; shortened form H-bomb is from 1950.
hydrogenate (v.) Look up hydrogenate at Dictionary.com
"cause to combine with hydrogen," 1809, from hydrogen + -ate (2). Related: Hydrogenated; hydrogenation.
hydrogeology (n.) Look up hydrogeology at Dictionary.com
also hydro-geology, 1802, from hydro- + geology; modeled on French hydrogéologie.
hydrography (n.) Look up hydrography at Dictionary.com
"science of the measurement and description of the sea," 1550s, from hydro- + -graphy. Related: Hydrographic.
hydrology (n.) Look up hydrology at Dictionary.com
"the science of water," 1762, from hydro- + -logy. Related: Hydrologist; hydrological (1660s).
hydrolysis (n.) Look up hydrolysis at Dictionary.com
"chemical decomposition by water," 1879, formed in English from hydro- + Greek lysis "a loosening, a dissolution," from lyein "to loosen, dissolve" (see lose). Related: Hydrolitic (1875).
hydrometer (n.) Look up hydrometer at Dictionary.com
1670s, from hydro- + meter (n.3). Related: Hydrometric; hydrometry.
hydrophobia (n.) Look up hydrophobia at Dictionary.com
late 14c., idroforbia, "dread of water, aversion to swallowing water," a symptom of rabies in man (sometimes used for the disease itself), from Late Latin hydrophobia, from Greek hydrophobos "dreading water," from hydr-, stem of hydor "water" (see water (n.1)) + phobos "dread, fear" (see phobia). So called because human sufferers show aversion to water and have difficulty swallowing it. In Old English as wæterfyrhtness. Related: Hydrophobe.
hydrophobic (adj.) Look up hydrophobic at Dictionary.com
1807, from hydrophobia + -ic.
hydroplane (v.) Look up hydroplane at Dictionary.com
by 1908, "to skim the surface of water by use of hydroplanes," from hydroplane (n.). Meaning "skid on a thin layer of water" (especially of automobile tires) first recorded 1962, properly aquaplane (itself from 1961 in this sense). Related: Hydroplaned; hydroplaning.
hydroplane (n.) Look up hydroplane at Dictionary.com
"motorboat that glides on the surface of water," 1895, coined by U.S. engineer Harvey D. Williams ["Sibley Journal of Engineering," Cornell University, vol. x, p.81]; from hydro- + ending from airplane.
hydroponics (n.) Look up hydroponics at Dictionary.com
"process of growing plants without soil," 1937, formed in English from hydro- + -ponics, from Greek ponein "to labor, toil," from ponos "labor" (see span (v.)). Related: Hydroponic (adj.).
hydropower (n.) Look up hydropower at Dictionary.com
1922, from hydro- (short for hydro-electric) + power (n.).
hydropsy (n.) Look up hydropsy at Dictionary.com
see dropsy.
hydrosphere (n.) Look up hydrosphere at Dictionary.com
"the waters of the Earth's surface," 1870, from hydro- + sphere.
hydrostatic (adj.) Look up hydrostatic at Dictionary.com
"pertaining to the principles of equilibrium of fluids," 1670s, from hydro- "water" + -static "stabilizing" (see -stat). Related: Hydrostatics (1650s); hydrostatical.
hydrotherapy (n.) Look up hydrotherapy at Dictionary.com
1842, from hydro- "water" + therapy. Related: Hydrotherapeutic.
hydrothermal (adj.) Look up hydrothermal at Dictionary.com
"of or pertaining to heated water," 1855, in geology, from hydro- "water" + thermal (adj.).
hydrous (adj.) Look up hydrous at Dictionary.com
"containing water," 1812; see hydro- + -ous.
hydroxide (n.) Look up hydroxide at Dictionary.com
1830, from French hydroxide; see hydro- + oxide.
Hydrus Look up Hydrus at Dictionary.com
1660s as a fabulous water serpent; 1670s as a southern constellation; from Latin Hydrus, from Greek hydros "water-snake" (see hydra).
hyena (n.) Look up hyena at Dictionary.com
mid-14c., from Old French hiene, from Latin hyaena, from Greek hyaina "hyena," apparently a fem. formation from hys "pig," from PIE *su- "swine" (see sow (n.)). With fem. suffix -aina. So called for its bristles. Applied to cruel, treacherous, and greedy persons since at least 1670s. Adjectival forms that have been attempted in English include hyenaish, hyenaesque, hyenic, hyenine, hyenoid.
hyetal (adj.) Look up hyetal at Dictionary.com
"of or relating to rain," 1855, American English, from Greek hyetos "rain" (see hyeto-) + -al (1).
hyeto- Look up hyeto- at Dictionary.com
word-forming element in science meaning "rain," from Greek hyetos "rain," from hyein "to rain," from PIE root *seue- (2) "take liquid" (see sup (v.2)).
hygiene (n.) Look up hygiene at Dictionary.com
1670s, from French hygiène, ultimately from Greek hygieine techne "the healthful art," from hygies "healthy, sound, hearty," literally "living well" (personified as the goddess Hygieia), from PIE *eyu-gwie-es- "having a vigorous life," from root *aiw-, *ayu- "vital force, life, long life, eternity; in the prime of life, young" (source of Latin aevus, English ever; see eon). The Greek adjective was used by Aristotle as a noun meaning "health." The difficult spelling in English is a relic of the struggle to render the Greek vowels into French.
hygienic (adj.) Look up hygienic at Dictionary.com
1815, from French hygiénique (1812), from hygiène (see hygiene). The earlier adjective was hygienal (1660s). Related: Hygienics (1836).
hygienist (n.) Look up hygienist at Dictionary.com
1836, "an expert on cleanliness," from hygiene + -ist. Earlier was hygeist (1716). Dental sense is recorded by 1913.
hygro- Look up hygro- at Dictionary.com
word-forming element meaning "wet, moist; moisture," from Greek hygros "wet, moist, fluid."
hygrology (n.) Look up hygrology at Dictionary.com
"science of bodily humors," 1787, from French or German hygrologie, which are earlier, or from hygro- "wet, moist; moisture" + -ology.
hygrometer (n.) Look up hygrometer at Dictionary.com
"instrument for measuring atmospheric moisture," 1660s, from French hygromètre, from Greek hygro- "wet, moist; moisture" (see hygro-) + -meter. Related: Hygrometry; hygrometric.
hygroscope (n.) Look up hygroscope at Dictionary.com
"device which indicates atmospheric humidity," 1660s, from hygro- "wet, moist; moisture" + -scope. It indicates the presence of moisture but not the amount (which is measured by a hygrometer). Related: Hygroscopic.
Hyksos Look up Hyksos at Dictionary.com
c. 1600, 15th dynasty of Egyptian kings (1650-1558 B.C.E.), called "Shepherd Kings," from Greek Hyksos, from Egyptian, explained variously as hiq shasu "ruler of nomads," or heqa khoswe "chief of foreign lands."
hylo- Look up hylo- at Dictionary.com
word-forming element meaning "wood, forest," also "matter," from Greek hylos "a wood, a forest, woodland; wood, firewood, timber; stuff, material," used by Aristotle for "matter" in the philosophical sense; a word of unknown origin.
Hyman Look up Hyman at Dictionary.com
masc. proper name; see Hymie.
hymen (n.) Look up hymen at Dictionary.com
1610s, from French hymen (16c.), from medical Latin, ultimately from Greek hymen "membrane (especially 'virginal membrane,' as the membrane par excellence); thin skin," from PIE *syu-men-, from root *syu- "to bind, sew" (see sew). Specific modern medical meaning begins with Vesalius in the 1555 edition of "De humani corporis fabrica." Apparently not directly connected to Hymen, the god of marriage, but sharing the same root and in folk etymology supposed to be related. Related: Hymenial.
Hymen Look up Hymen at Dictionary.com
1580s, Greek god of marriage, represented as a youth carrying a torch and a veil, perhaps etymologically "the joiner," literally "the one who sews" (two together); see hymen. Related: Hymeniac.
hymeneal (adj.) Look up hymeneal at Dictionary.com
c. 1600, "of or relating to a marriage," with -al (1) + Hymen, Greek god of marriage. Compare Latin hymenaeus, from Greek hymenaios "belonging to wedlock;" also as a noun "wedding, wedding song." As a noun in English, "wedding hymn," from 1717.
hymeno- Look up hymeno- at Dictionary.com
word-forming element used in technical and scientific compounds, "membrane," from Greek hymen "membrane" (see hymen).
Hymenoptera Look up Hymenoptera at Dictionary.com
order of insects that includes ants, wasps, and bees, 1773, coined in Modern Latin 1748 by Linnæus from Greek hymen (genitive hymenos) "membrane" (see hymen) + pteron "wing" (see ptero-). Related: Hymenopterous.
hymie (n.) Look up hymie at Dictionary.com
"Jewish male" (derogatory), by early 1980s, apparently originally African-American vernacular, from common Jewish masc. proper name Hymie, a pet form of Hyman, from Hebrew, literally "life" (the masc. counterpart of Eve).
hymn (n.) Look up hymn at Dictionary.com
"religious song," c. 1000, from Old French ymne and Old English ymen, both from Late Latin hymnus "song of praise," from Greek hymnos "festive song or ode in praise of gods or heroes" (also sometimes of mournful songs), used in Septuagint to translate several Hebrew words meaning "song praising God." Possibly a variant of hymenaios "wedding song," from Hymen, Greek god of marriage, or, as per Watkins, from a PIE root *sam- "to sing" (source also of Hittite išhamai "he sings," Sanskrit saman- "hymn, song"). Evidence for the silent -n- dates from at least 1530.
hymnal (n.) Look up hymnal at Dictionary.com
c. 1500, imnale, himnale, "hymn-book," from Medieval Latin hymnale (n.), from ymnus, from Latin hymnus "song of praise" (see hymn). As an adjective, "of or pertaining to hymns," attested from 1640s.

Hymnal measure (a quatrain, usually iambic, alternately rhymed) is so called for being the preferred verse form for English hymns (such as "Amazing Grace"). It has been popular in English secular poetry as well, "though it almost always suggests the hymn, directly or ironically" [Miller Williams, "Patterns of Poetry," 1986].
hymnic (adj.) Look up hymnic at Dictionary.com
1580s, from hymn + -ic.
hymnist (n.) Look up hymnist at Dictionary.com
1620s, from hymn + -ist.
hyoid (adj.) Look up hyoid at Dictionary.com
"having the form of the Greek capital letter upsilon" (ϒ), 1811, from French hyoïde (16c.), from Modern Latin hyoides, from Greek hyoeides "shaped like the letter U," from hu "letter U" (in later Greek called upsilon) + -oeides "like" (see -oid).
hype (n.) Look up hype at Dictionary.com
"excessive or misleading publicity or advertising," 1967, American English (the verb is attested from 1937), probably in part a back-formation of hyperbole, but also from underworld slang verb hype "to swindle by overcharging or short-changing" (1926), itself a back-formation from hyper "short-change con man" (1914), from the prefix hyper- meaning "over, to excess."

Also possibly influenced by drug addicts' slang hype, shortening of hypodermic needle (1913). Related: Hyped; hyping. In early 18c., hyp "morbid depression of the spirits" was colloquial for hypochondria (usually as the hyp or the hyps).
hyper (adj.) Look up hyper at Dictionary.com
1942 as a colloquial shortening of hyperactive.
hyper- Look up hyper- at Dictionary.com
word-forming element meaning "over, above, beyond," and often implying "exceedingly, to excess," from Greek hyper (prep. and adv.) "over, beyond, overmuch, above measure," from PIE *uper "over" (see super-).
hyperactive (adj.) Look up hyperactive at Dictionary.com
1852, from hyper- "over, exceedingly, to excess" + active.
hyperactivity (n.) Look up hyperactivity at Dictionary.com
1852, from hyper- "over, exceedingly, to excess" + activity.