zoological (adj.) Look up zoological at Dictionary.com
1807, from zoology + -ical.
zoologist (n.) Look up zoologist at Dictionary.com
1660s, from zoology + -ist.
zoology (n.) Look up zoology at Dictionary.com
"science of animals," 1660s, from Modern Latin zoologia, from Greek zoion "animal" (see zoo-) + -logia "study" (see -logy).
zoom (v.) Look up zoom at Dictionary.com
1886, of echoic origin. Gained popularity c.1917 as aviators began to use it. As a noun from 1917. The photographer's zoom lens is from 1936, from the specific aviation sense of zoom as "to quickly move closer."
zoomorphic (adj.) Look up zoomorphic at Dictionary.com
"representative of animals," especially representative of a god in the form of an animal, 1872, from zoo- + morphe "shape" (see Morpheus) + -ic. Related: Zoomorphism.
zoon (n.) Look up zoon at Dictionary.com
"animal form containing all elements of a typical organism of its group," 1864, from Greek zoion "animal" (see zoo-).
zoonosis (n.) Look up zoonosis at Dictionary.com
"disease communicated to humans by animals," plural zoonoses, 1876, from zoo- "animal" + nosos "disease" (see noso-).
zoonotic (adj.) Look up zoonotic at Dictionary.com
1900, from zoonosis + -ic.
zoophagous (adj.) Look up zoophagous at Dictionary.com
"carnivorous," 1840, from zoo- + -phagous. Related: Zoophagy; zoophage.
zoophilia (n.) Look up zoophilia at Dictionary.com
"attraction to animals involving release of sexual energy," 1899, in a translation of Krafft-Ebing, from zoo- "animal" + -philia. "[F]ormerly not implying sexual intercourse or bestiality" [OED]. The meaning "sympathy or tender care for living creatures" is in the nativized formation zoophily (1886).
zoophobia (n.) Look up zoophobia at Dictionary.com
1901, from zoo- "animal" + -phobia. Related: Zoophobic; zoophobe.
zooplankton (n.) Look up zooplankton at Dictionary.com
1901, from zoo- "animal" + plankton.
zoot suit (n.) Look up zoot suit at Dictionary.com
1942, American English slang, the first element probably a nonsense reduplication of suit (compare reet pleat, drape shape from the same jargon).
zooxanthella (n.) Look up zooxanthella at Dictionary.com
plural zooxanthellae, yellow pigmentary particles found in nature, 1889, from German (Brandt, 1881), from comb. form of Greek zoion "animal" (see zoo-) + xantho- "yellow" (see xantho-) + Latin suffix -ella.
zori (n.) Look up zori at Dictionary.com
1823, from Japanese zori, from so "grass, (rice) straw" + ri "footwear, sole."
Zoroastrian (adj.) Look up Zoroastrian at Dictionary.com
1743, from Zoroaster, from Latin Zoroastres, from Old Persian Zarathushtra, 6c. or 7c. B.C.E. Persian religious teacher. The name appears to be literally "whose camels are old," from *zarant "old" (cognate with Greek geron, genitive gerontos "old;" see gerontology) + ushtra "camel." As a noun from 1811.
Zoroastrianism (n.) Look up Zoroastrianism at Dictionary.com
1854, from Zoroastrian + -ism.
zorro (n.) Look up zorro at Dictionary.com
1838, "South American fox-wolf," from Spanish zorro, masc. of zorra "fox," from Basque azaria "fox." The comic book hero, a variation on the Robin Hood theme set in old Spanish California, was created 1919 by U.S. writer Johnston McCulley (1883-1958).
zoster (n.) Look up zoster at Dictionary.com
kind of seaweed, c.1600, Latin, from Greek zoster "girdle," originally "warrior's belt," from zonnynai (see zone (n.)). Meaning "shingles" is from 1706; in the literal sense, "a belt or girdle, especially for men," from 1824.
zouave (n.) Look up zouave at Dictionary.com
member of a French light infantry troop, 1848, from French, from Arabic Zwawa, from Berber Igawawaen, name of a Kabyle tribe in Algeria, from which the zouaves originally were recruited in 1831. The military units soon became exclusively French but served only in Algeria until 1854 and were "distinguished for their dash, intrepidity, and hardihood, and for their peculiar drill and showy Oriental uniform" [Century Dictionary]. Some Northern regiments in the American Civil War adopted the name and elements of the uniform. The women's fashionable zouave jacket (1859) also is based on the uniform.
zouk (n.) Look up zouk at Dictionary.com
Creole French, "party," from zouker "engage in unrestrained social activity."
zounds (interj.) Look up zounds at Dictionary.com
c.1600, oath of surprise or anger, altered from (by) God's wounds!, in reference to the wounds of Christ on the Cross. "One of the innumerable oaths having reference to Christ's passion" [Century Dictionary]. Compare gadzooks.
zowie (interj.) Look up zowie at Dictionary.com
expression of astonishment, c.1913.
zucchetto (n.) Look up zucchetto at Dictionary.com
small, round skull-cap worn by dignitaries in the Catholic Church, 1853, from Italian zucchetta "a cap," originally diminutive of zucca "gourd, head," perhaps from Late Latin cucutia, of unknown origin.
zucchini (n.) Look up zucchini at Dictionary.com
1915 in English cookery books, 1910 in travel books about Italy as an Italian word (defined as "an odd kind of little squash, very tender and palatable"), from Italian, plural of zucchino, diminutive of zucca "gourd, squash," perhaps from Late Latin cucutia, which is of unknown origin.
Zulu (n.) Look up Zulu at Dictionary.com
one of a Bantu people of South Africa, 1824, a native name. As radio code word for -z- from 1960.
Zuni (n.) Look up Zuni at Dictionary.com
native people and language of New Mexico, 1834, from Spanish, from a local native word.
Zurich Look up Zurich at Dictionary.com
city and lake in Switzerland, German Zürich, said to be ultimately from Celtic root *dur- "water."
zwieback (n.) Look up zwieback at Dictionary.com
1894, from German Zweiback "biscuit," literally "twice-baked," from zwei "two, twice" + backen "to bake;" loan-translation of Italian biscotto (see biscuit).
Zwinglian (adj.) Look up Zwinglian at Dictionary.com
1532, after Ulrich Zwingli (1484-1531), Swiss Protestant reformer who revolted from the Roman communion in 1516 but who differed from Luther on theological points relating to the real presence in the Eucharist.
zydeco (n.) Look up zydeco at Dictionary.com
1949, perhaps from Creole French pronunciation of French les haricots "the beans," part of the title of a popular dance tune ("les haricots sont pas salés").
zygoma (n.) Look up zygoma at Dictionary.com
"bony arch of the cheek," plural zygomata, 1680s, Modern Latin, from Greek zygoma, from zygon "yoke" (see jugular). So called because it connects the bones of the face with those of the skull about the ear.
zygomatic (adj.) Look up zygomatic at Dictionary.com
"pertaining to the zygoma," 1709, from Latin zygomaticus, from Greek zygoma (see zygoma).
zygote (n.) Look up zygote at Dictionary.com
1880, coined 1878 by German cytologist Eduard Strasburger (1844-1912), the widespread attribution to William Bateson being apparently erroneous; from Greek zygotos "yoked," from zygon "yoke" (see jugular).
Zyklon (n.) Look up Zyklon at Dictionary.com
type of fumigant used to kill rats in enclosed spaces, such as holds of ships, boxcars, etc., 1926, from German Zyklon, commercial name of a type of hydrogen cyanide, said to be of unknown etymology, but it is the usual German form of the word cyclone. There were at least three varieties, A, B, and C, Zyklon-B being the one notoriously used in the Nazi death camps.
zymurgy (n.) Look up zymurgy at Dictionary.com
branch of chemistry which deals with wine-making and brewing, 1868, from Greek zymo-, comb. form of zyme "a leaven" (from PIE root *yeue-; see juice) + -ourgia "a working," from ergon "work" (see organ).

The last word in many standard English dictionaries (and this one); but Century Dictionary ends with Zyxomma ("A genus of Indian dragon-flies") and in the OED [2nd ed.] the last word is zyxt, an obsolete Kentish form of the second person singular of see (v.).
At the dictionary's letter A
Mr. Brandt is young and gay
But when at last he reaches zed
He's in his wheelchair, nearly dead

[Einar Haugen]