Online Etymology Dictionary

amethyst (n.): violet quartz, late 13c., ametist, from Old French ametiste (Modern French améthyste) and directly from Medieval Latin amatistus, from Latin amethystus, from Greek amethystos "amethyst," literally "not intoxicating," from a- "not" + methyskein "make drunk," from methys "wine" (see mead (n.1)); based on the stone's ancient reputation for preventing drunkenness, which was perhaps sympathetic magic suggested by its wine-like color. People wore rings made of it before drinking. Spelling restored from Middle English ametist.
Amex: blend of American Express, trademark registered in U.S. 1950 by American Express Co., originally an express mail service. Its credit card dates from 1958.
Amharic: principal language of Ethiopia, 1813, from Amhara, name of a central province in Ethiopia.
ami (n.): 14c., "friend lover," from Old French amy, ami (see Amy).
amiability (n.): 1807; see amiable + -ity. Amiableness is recorded from 1530s.
amiable (adj.): mid-14c., from Old French amiable, from Late Latin amicabilis "friendly," from amicus "friend," related to amare "to love" (see Amy). The form confused in Old French with amable "lovable," from Latin amare. Reborrowed later in proper Latin form as amicable.
amicability (n.): 1650s, see amicable + -ity.
amicable (adj.): early 15c., from Late Latin amicabilis "friendly," a word in Roman law, from Latin amicus "friend," related to amare "to love" (see Amy). Also see amiable.
amicably (adv.): 1630s, from amicable + -ly (2).
amicus curiae: 1610s, Latin, literally "friend of the court;" plural is amici curiae. From Latin amicus "friend," related to amare "to love" (see Amy) + curia "court" (see curia).
amid (prep.): late 14c., from amidde (c. 1200), from Old English on middan "in the middle," from dative singular of midde "mid, middle" (see middle); the phrase evidently was felt as "in (the) middle" and thus followed by a genitive case, and if this had endured we would follow it today with of. (See amidst for further evolution along this line).

The same applies to equivalents in Latin (in medio) and Greek (en meso), both originally adjective phrases which evolved to take the genitive case. But in later Old English on middan also was treated as a preposition and followed by dative. Used in compounds from early 13c. (such as amidships, attested from 1690s and retaining the genitive, as the compounds usually did in early Middle English, suggesting this one is considerably older than the written record of it.)
amidst (prep.): a variant of amid (q.v.) with adverbial genitive -s and parasitic -t. Amidde became amyddes (13c.) and acquired a -t by 1560s, probably by association with superlatives in -st.
There is a tendency to use amidst more distributively than amid, e.g. of things scattered about, or a thing moving, in the midst of others. [OED]
amigo (n.): "friend, comrade," often a form of address, 1837, American English (first attested in the phrase adios, Amigo), from Spanish amigo, literally "friend," from Latin amicus "friend," related to amare "to love" (see Amy).
amine (n.): "compound in which one of the hydrogen atoms of ammonia is replaced by a hydrocarbon radical," 1863, from ammonia + chemical suffix -ine (2).
amino-: 1887, as an element in compound words involving chemicals, from comb. form of amine. Amino acid is attested from 1898.
amir (n.): 1610s; the same word as emir (q.v.), but generally used of contemporary Indian or Afghan rulers as opposed to historical ones.
Amish (adj.): 1844, American English, from the name of Jacob Amman, 17c. Swiss Mennonite preacher who founded the sect. Originally spelled Omish, which reflects the pronunciation in Pennsylvania German dialect. As a noun, by 1884.
amiss (adv.): mid-13c., amis "off the mark," also "out of order," literally "on the miss," from a "in, on" (see a- (1)) + missen "fail to hit" (see miss (v.)). To take (something) amiss originally (late 14c.) was "to miss the meaning of" (see mistake). Now it means "to misinterpret in a bad sense."
amity (n.): mid-15c., "friendly relations," from Old French amitie (13c.); earlier amistie (11c.), from Vulgar Latin *amicitatem (nominative *amicitas) "friendship," corresponding to Latin amicitia, from amicus (adj.) "friendly;" related to amare "to love" (see Amy).
ammeter (n.): instrument for measuring the strength of electric currents, 1882, from ampere + -meter.
ammo (n.): 1917, shortened form of ammunition.
ammonia (n.): 1799, Modern Latin, coined 1782 by Swedish chemist Torbern Bergman (1735-1784) for gas obtained from sal ammoniac, salt deposits containing ammonium chloride found near temple of Jupiter Ammon (from Egyptian God Amun) in Libya, from Greek ammoniakos "belonging to Ammon." The shrine was ancient already in Augustus' day, and the salts were prepared "from the sands where the camels waited while their masters prayed for good omens" [Shipley].

There also was a gum form of sal ammoniac, from a wild plant that grew near the shrine, and across North Africa and Asia. A less likely theory traces the name to Greek Armeniakon "Armenian," because the substance also was found in Armenia. Also known as spirit of hartshorn and volatile or animal alkali.
ammonite (n.): "cephalopod mollusk," 1758, from French (Breyn, 1732), "better established" [Century Dictionary] by French zoologist Jean Guillaume Bruguière (c. 1750-1798) in 1789, from Medieval Latin (cornu) Ammonis "horn of Ammon," the Egyptian god of life and reproduction, who was depicted with ram's horns, which the fossils resemble. The resemblance also was noted in ancient times.
ammunition (n.): 1620s, from French soldiers' faulty separation of Middle French la munition into l'ammunition; from Latin munitionem (nominative munitio) "a fortifying" (see munition), and at first meaning all military supplies in general. The mistake in the word perhaps was by influence of French a(d)monition "warning." The error was corrected in French (Modern French munition), but retained in English.
amnesia (n.): "loss of memory," 1786 (as a Greek word in English from 1670s), Modern Latin, coined from Greek amnesia "forgetfulness," from a-, privative prefix, "not" (see a- (3)) + stem from mnasthai "to recall, remember," related to mnemnon "mindful," mneme "memory;" from PIE root *men- "to think, remember" (see mind (n.)).
amnesiac (n.): "one affected by amnesia," 1913, from amnesia (q.v.).
amnesic (adj.): "pertaining to amnesia," 1863; see amnesia + -ic.
amnestic (adj.): "causing loss of memory," 1879, from Greek amnestia "oblivion, forgetfulness;" see amnesia.
amnesty (n.): "pardon of past offenses," 1570s, from French amnestie "intentional overlooking," from Latin amnestia, from Greek amnestia "forgetfulness (of wrong); an amnesty," from a-, privative prefix, "not" (see a- (3)), + mnestis "remembrance," related to mnaomai "I remember" (see mind (n.)). As a verb, from 1809. Amnesty International founded 1961 as Appeal for Amnesty. The name was changed 1963.
amniocentesis (n.): 1958, Modern Latin, from amnion (see amniotic) + centesis "surgical puncture," from Greek kentesis "a pricking," from kentein "to prick," related to kontos "pole" (see center (n.)).
amnion (n.): 1660s, Modern Latin, from Greek amnion "membrane around a fetus," said to be originally "bowl in which the blood of victims was caught" [Liddell & Scott], which is variously said to be of unknown origin, from ame "bucket," or a diminutive of amnos "lamb."
amniotic (adj.): 1822, from Modern Latin amnion (see amnion) + -ic.
amoeba (n.): 1855, from Modern Latin Amoeba, genus name (1841), from Greek amoibe "change," related to ameibein "to change, exchange," from PIE *e-meigw-, extended form of root *mei- (1) "to change, go, move" (see mutable). So called for its constantly changing shape. Related: Amoebaean; amoebic.
amoebae: classical plural of amoeba; see -ae.
amok (adv.): in verbal phrase run amok first recorded 1670s, from Malay amuk "attacking furiously." Earlier the word was used as a noun or adjective meaning "a frenzied Malay," originally in the Portuguese form amouco or amuco.
There are some of them [the Javanese] who ... go out into the streets, and kill as many persons as they meet. ... These are called Amuco. ["The Book of Duarte Barbosa: An Account of the Countries Bordering on the Indian Ocean and Their Inhabitants," c. 1516, English translation]
Compare amuck.
amole (n.): 1831, from Mexican Spanish amole, from Nahuatl (Aztecan) amolli "soap-root."
among (prep.): early 12c., from Old English onmang, from phrase on gemang "in a crowd," from gemengan "to mingle" (see mingle). Collective prefix ge- dropped 12c. leaving onmong, amang, among. Compare Old Saxon angimang "among, amid;" Old Frisian mong "among."
amongst (prep.): mid-13c., amonges, from among with adverbial genitive. Parasitic -t first attested 16c. (see amidst). It is well established in the south of England, but not much heard in the north. By similar evolutions, alongst also existed in Middle English.
amontillado (n.): a variety of sherry wine, 1825, from Spanish amontillado, from a "from" (from Latin ad; see ad-) + Montilla, name of a town in the province of Cordova. Formerly the name of a regional wine, now of a type of sherry.
amoral (adj.): "ethically indifferent," 1882, a hybrid formed from Greek privative prefix a- "not" (see a- (3)) + moral, which is derived from Latin. First used by Robert Louis Stephenson (1850-1894) as a differentiation from immoral.
amoretto (n.): 1590s, from Italian, literally "little love," a diminutive of amore "love" (see Amy). This word was variously applied to love sonnets, cupids, etc. Also compare Amaretto.
amorous (adj.): c. 1300, from Old French amorous (Modern French amoureux), from Late Latin amorosum, from amor "love," from amare "to love" (see Amy). Related: Amorously; amorousness.
amorphous (adj.): "shapeless," 1731, from Modern Latin amorphus, from Greek amorphos "without form, shapeless, deformed," from a- "without" (see a- (3)) + morphe "form" (see Morpheus). Related: Amorphously; amorphousness.
amortisation (n.): chiefly British English spelling of amortization; see -ize.
amortise (v.): chiefly British English spelling of amortize; for suffix, see -ize. Related: Amortised; amortising.
amortization (n.): 1670s, in reference to lands given to religious orders, from Medieval Latin amortizationem (nominative amortizatio), noun of action from past participle stem of amortizare (see amortize). Of debts, from 1824.
amortize (v.): late 14c., from Old French amortiss-, present participle stem of amortir "deaden," from Vulgar Latin *admortire "to extinguish," from ad- "to" (see ad-) + mortus "dead," from Latin mors "death" (see mortal (adj.)). Originally a legal term for an act of alienating lands. Meaning "extinguish a debt" (in form amortization) is attested from 1824. Related: Amortized; amortizing.
Amos: masc. proper name; third of the prophets in the Old Testament; from Greek, from Hebrew Amos, literally "borne (by God)."
amount (v.): late 13c., "to go up, rise, mount (a horse)," from Old French amonter, from a mont "upward," literally "to the mountain," from Latin ad- "to" (see ad-) + montem (nominative mons) "mountain" (see mount (n.1)). Meaning "to rise in number or quality (so as to reach)" is from c. 1300. Related: Amounted; amounting.
amount (n.): 1710, from amount (v.).