Online Etymology Dictionary

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)) + mimneskesthai "to recall, cause to remember," a reduplicated form related to Greek mnemnon "mindful," mneme "memory," mnasthai "to remember;" 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- "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]
Cf. amuck.
amole (n.): 1831, from Mexican Spanish amole, from Nahuatl (Aztec) 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. Cf. 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 cf. 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 (n.): 1710, from amount (v.).
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.)). Meaning "to rise in number or quality (so as to reach)" is from c.1300. Related: Amounted; amounting.
amour (n.): c.1300, "love," from Old French amour, from Latin amorem (nominative amor) "love, affection, strong friendly feeling" (it could be used of sons or brothers, but especially of sexual love), from amare "to love" (see Amy). The accent shifted 15c.-17c. to the first syllable as the word became nativized, then shifted back as the naughty or intriguing sense became primary and the word was felt to be a euphemism.
A common ME word for love, later accented ámour (cf. enamour). Now with suggestion of intrigue and treated as a F[rench] word. [Weekley]
amour-propre (n.): 1775, French, "sensitive self-love, self-esteem;" see amour and proper.
Vanity usually gives the meaning as well, &, if as well, then better. [Fowler]
The term was in Middle English as proper love "self-love."
amoxycillin (n.): 1971, contracted from amino- + oxy- + ending from penicillin.
Amoy: old name for the island of southeastern China, now known as Xiamen. From 1851 as the name of a dialect of Chinese.
amp (n.): 1886 as an abbreviation of ampere; 1967 as an abbreviation of amplifier.
amperage (n.): strength of an electric current, 1894, from ampere on model of voltage.
ampere (n.): 1881, "the current that one volt can send through one ohm," from French ampère, named for French physicist André-Marie Ampère (1775-1836). Shortened form amp is attested from 1886.
ampersand (n.): 1837, contraction of and per se and, meaning "(the character) '&' by itself is 'and' " (a hybrid phrase, partly in Latin, partly in English). The symbol is based on the Latin word et "and," and comes from an old Roman system of shorthand signs (ligatures), attested in Pompeiian graffiti, but not (as sometimes stated) from the Tironian Notes, which was a different form of shorthand, probably invented by Cicero's companion Marcus Tullius Tiro, which used a different symbol, something like a reversed capital gamma, to indicate et.

This Tironian symbol was maintained by some medieval scribes, including Anglo-Saxon chroniclers, who sprinkled their works with a symbol like a numeral 7 to indicate the word and. In old schoolbooks the ampersand was printed at the end of the alphabet and thus by 1880s had acquired a slang sense of "posterior, rear end, hindquarters."
amphetamine (n.): 1938, contracted from alphamethyl-phenethylamine.
amphi-: before a vowel amph-, word-forming element from Greek amphi- "both, of both kinds, on both sides, around," comb. form of amphi "round about, around;" cognate with Latin ambi- (see ambi-).
amphibian (adj.): 1630s, "having two modes of existence, of doubtful nature," from Greek amphibia, neuter plural of amphibios "living a double life," from amphi- "of both kinds" (see amphi-) + bios "life" (see bio-).

Formerly used by zoologists to describe all sorts of combined natures (including otters and seals), the biological sense "class of animals between fishes and reptiles that live both on land and in water" and the noun derivative both are first recorded 1835. Amphibia was used in this sense from c.1600 and has been a zoological classification since c.1819.
amphibious (adj.): 1640s, from Greek amphibios "having a double life" (see amphibian). Of motor vehicles, from 1915.
amphibrach (n.): 1580s, from Latin amphibrachus, from Greek amphibrakhys, a foot consisting of a long syllable between two short, literally "short at both ends," from amphi- "on both sides" (see amphi-) + brakhys "short" (see brief (adj.)).
Amphictyonic League: 1753, one of several ancient Greek confederations of neighboring states, from Greek amphiktionikos, from amphiktiones "neighbors," literally "they that dwell round about," from amphi- "on both sides" (see amphi-) + second element related to ktizein "to create, found," ktoina "habitation, township," from PIE root *tkei- "to settle, dwell, be home" (see home (n.)).
amphigory (n.): 1809, "burlesque nonsense writing or verse," from French amphigouri, of unknown origin, perhaps from Greek amphi- (see amphi-) + gyros "circle," thus "circle on both sides," or second element may be from Greek -agoria "speech" (cf. allegory, category). Related: Amphigoric.
Amphiscians (n.): 1620s, from Medieval Latin Amphiscii, from Greek amphiskioi "inhabitants of the tropics," literally "throwing a shadow both ways," from amphi- "on both sides" (see amphi-) + skia "shadow" (see shine (v.)). Inhabitants of torrid zones, so called because they are "people whose shadow is sometimes to the North, and sometimes to the South" [Cockerham, 1623].
amphitheater (n.): late 14c., from Latin amphitheatrum, from Greek amphitheatron "double theater, amphitheater," neuter of amphitheatros "with spectators all around," from amphi- "on both sides" (see amphi-) + theatron "theater" (see theater). Classical theaters were semi-circles, thus two together made an amphi-theater.
amphitheatre (n.): chiefly British English spelling of amphitheater. See -er.
amphora (n.): early 14c., "two-handled vessel for holding wine, oil, etc.," from Latin amphora from Greek amphoreus "an amphora, jar, urn," contraction of amphiphoreus, literally "two-handled," from amphi- "on both sides" (see amphi-) + phoreus "bearer," related to pherein "to bear" (see infer). Also a liquid measure in the ancient world, in Greece equal to 9 gallons, in Rome to 6 gallons, 7 pints.
amphoteric (adj.): "neither acid nor alkaline," 1832, from Greek amphoteros "each or both of two," variant of amphi-.