Online Etymology Dictionary

Z: not a native letter in Old English; in Anglo-French words it represents the "ts" sound (e.g. Anglo-French fiz, from Latin filius, modern Fitz); from late 13c. it began to be used for the voiced "s" sound and had fully taken that role by 1400. For letter name, see zed.
Thou whoreson Zed, thou vnnecessary Letter. ["King Lear," II.ii.69]
Series of zs to represent a buzzing sound first attested 1852; zees "spell of sleep, a nap" is slang first recorded 1963, American English student slang.
za (n.): U.S. student slang shortening of pizza, attested from 1968.
Zacchaeus: masc. proper name, from Late Latin Zacchaeus, from Greek Zakkhaios, from Hebrew zakkay, literally "pure, innocent," from zakhah "was clean, was pure."
Zachariah: masc. proper name, Late Latin Zacharias, from Greek Zakharias, from Hebrew Zekharyahu, literally "the Lord has remembered," from zakhar "he remembered."
zaftig (adj.): "alluringly plump, curvaceous, buxom," 1937, from Yiddish zaftik, literally "juicy," from zaft "juice," from Middle High German saft "juice" (see sap (n.1)).
zag (v.): 1793, from zig-zag (q.v.).
zaibatsu: 1937, from Japanese zaibatsu, from zai "wealth" + batzu "clique."
Zaire: African nation (1971-1997), from an early alternative name of the Congo River, from Kikongo nzai, dialectal form of nzadi "river."
zakat (n.): 1802, from Persian zakat, etc., from Arabic zakah.
Zamboni (n.): proprietary name for a machine used to resurface ice skating rinks, 1965, trademark of Frank J. Zamboni & Co., Paramount, Calif., claiming use since July 1962.
zany (n.): comic performer, 1580s, from French zani, from Italian zani, zanni "a zany, clown," originally Zanni, Venetian dialect variant of Gianni, pet form of Giovanni "John." A stock character in old comedies, he aped the principal actors.
zany (adj.): 1869, from zany (n.). Related: Zanily; zaniness.
zap: 1929 as a sound, 1942 as a verb, comic strip word (especially from "Buck Rogers in the Twenty-Fifth Century"), of imitative origin. Meaning "to erase electronically" is 1982. Related: Zapped; zapping.
Zarathustra: from Avestan Zarathushtra (see Zoroastrian).
zarf (n.): 1836, from Arabic zarf "vessel."
zeal (n.): late 14c., from Late Latin zelus "zeal, emulation" (source of Old French zel, Italian zelo, Spanish celo), a Church word, from Greek zelos "zeal, ardor, jealousy," which is of uncertain origin.
zealot (n.): c.1300, "member of a militant 1st century Jewish sect which fiercely resisted the Romans in Palestine," from Late Latin Zelotes, from Greek zelotes "one who is a zealous follower," from zeloun "to be zealous," from zelos "zeal" (see zeal). Extended sense of "a fanatical enthusiast" first recorded 1630s.
zealotry (n.): 1650s, from zealot + -ry.
zealous (ad.): 1520s, from Medieval Latin zelosus (source of Italian zeloso, Spanish celoso), from zelus (see zeal). Related: Zealously, zealousness.
zebra (n.): c.1600, from Italian zebra, perhaps via Portuguese, earlier applied to a now-extinct wild ass, said to be Congolese [OED], or Amharic [Klein], but perhaps ultimately from Latin equiferus "wild horse," from equus "horse" (see equine) + ferus (see fierce).
zebu (n.): Asiatic ox, 1774, from French zebu, ultimately of Tibetan origin. First shown in Europe at the Paris fair of 1752.
Zebulon: masc. proper name, Biblical son of Jacob by Leah, from Hebrew Zebhulun, from zebhul "a dwelling" + diminutive suffix -on (cf. Gen. xxx:20).
Zechariah: masc. proper name, Biblical 11th of the Twelve Prophets; see Zachariah.
zed (n.): c.1400, from Middle French zede, from Late Latin zeta, from Greek zeta, from Hebrew zayin, letter name, literally "weapon;" so called in reference to the shape of this letter in ancient Hebrew. U.S. pronunciation zee is first attested 1670s. Other dialectal names for the letter are izzard, ezod, uzzard, and zod.
zee (n.): "the letter Z," 1670s, now more common in American English.
zein (n.): 1822, from zea, Late Latin name for "spelt," from Greek zeia.
Zeiss: in reference to spy-glasses or binoculars, 1905, from the firm founded by German optical instrument manufacturer Carl Zeiss (1816-1888).
zeitgeist (n.): 1848, from German Zeitgeist, literally "spirit of the age," from Zeit "time" (see tide) + Geist "spirit" (see ghost).
zek (n.): "Russian condemned person in a prison or labor camp," 1968, from Russian zek, probably representing a vocalization of z/k, abbreviation of zaklyuchennyi "prisoner."
Zen: school of Mahayana Buddhism, 1727, from Japanese, from Chinese ch'an, ultimately from Sanskrit dhyana "thought, meditation," from PIE root *dhya "to see, contemplate."
Zend: 1715, "Parsee sacred book" (in full, Zend-Avesta, 1620s), from Old Persian zend, from Pahlavi zand "commentary." First used in reference to the language of the Zend-Avesta in 1771 by Anquetiel-Duperron (1731-1805).
zenith (n.): late 14c., from Old French cenith (Modern French zénith), from Medieval Latin cenit, senit, bungled scribal transliterations of Arabic samt "road, path," abbreviation of samt ar-ras, literally "the way over the head." Letter -m- misread as -ni-.

The Medieval Latin word could as well be influenced by the rough agreement of the Arabic term with classical Latin semita "sidetrack, side path" (notion of "thing going off to the side"), from se- "apart" + *mi-ta-, suffixed zero-grade form of PIE root *mei- "to change" (see mutable).
zeno-: late 20c. word-forming element used in reference to the planet Jupiter, from Greek zeno-, comb. form from Zeus (see Zeus; also cf. Zenobia).
Zenobia: fem. proper name, from Greek Zenobia, literally "the force of Zeus," from Zen, collateral form of Zeus, + bia "strength, force," cognate with Sanskrit jya "force, power" (see Jain).
Zenonian (adj.): 1843, pertaining to one of two Greek thinkers: Zeno of Elea ("Zeno of the Paradoxes," 5c. B.C.E.), who disproved the possibility of motion; and Zeno of Citium (c. 300 B.C.E.), founder of stoicism.
zep (n.): abbreviation of zeppelin, attested by 1915.
zephyr (n.): mid-14c., from Old English Zefferus, from Latin Zephyrus, from Greek Zephyros "the west wind" (sometimes personified as a god), probably related to zophos "the west, the dark region, darkness, gloom." Sense of "mild breeze" is c.1600.
zeppelin (n.): 1900, from German Zeppelin, short for Zeppelinschiff "Zeppelin ship," after Count Ferdinand von Zeppelin (1838-1917), German general who perfected its design.
zero (n.): c.1600, from Italian zero, from Medieval Latin zephirum, from Arabic sifr "cipher," translation of Sanskrit sunya-m "empty place, desert, naught" (see cipher (n.)). A brief history of the invention of "zero" can be found here. Meaning "worthless person" is recorded from 1813. Zero tolerance first recorded 1972, originally U.S. political language.
zero (v.): in zero in, 1944, from zero (n.); the image is from instrument adjustments.
zest (n.): 1670s, from French zeste "piece of orange or lemon peel used as a flavoring," of unknown origin. Sense of "thing that adds flavor" is 1709; that of "keen enjoyment" first attested 1791.
zestful (adj.): 1797, from zest + -ful. Related: Zestfully; zestfulness.
zesty (adj.): 1789, from zest + -y (2). Related: Zestily; zestiness.
zeta: Greek letter, see zed.
zetetic (adj.): "proceeding by inquiry," 1640s, from Modern Latin zeteticus, from Greek zetetikos "searching, inquiring," from zetetos, verbal adjective of zetein "seek for, inquire into."
zeugma (n.): 1580s, "a single word (usually a verb or adjective) made to refer to two or more words in a sentence," from Greek, literally "a yoking," from zeugnynai "to yoke" (see jugular).
Zeus: supreme god of the ancient Greeks, 1706, from Greek, from PIE *dewos- "god" (cf. Latin deus "god," Old Persian daiva- "demon, evil god," Old Church Slavonic deivai, Sanskrit deva-), from root *dyeu- "to gleam, to shine;" also the root of words for "sky" and "day" (see diurnal). The god-sense is originally "shining," but "whether as originally sun-god or as lightener" is not now clear.
Ziegfeld: in reference to showgirls or stage revues, 1913, from Florenz Ziegfeld (1869-1932), U.S. theatrical producer, who staged annual "follies" from 1907-1931.
zig (v.): 1969, from zigzag.
zig-zag: also zigzag, 1712, from French zigzag (1670s), perhaps from German Zickzack (though this only is attested from 1703), possibly a reduplication of Zacke "tooth, prong." Earliest use in German is in reference to military siege approaches. Originally in English used to describe the layout of certain garden paths. The verb is recorded from 1787.