1530s (in Anglo-Latin from mid-13c.), via medieval French and Italian Assissini, Assassini, from Arabic hashīshīn (12c.), an Arabic nickname, variously explained, for the Nizari Ismaili sect in the Middle East during the Crusades, plural of hashishiyy, from the source of hashish (q.v.).
They were a fanatical Muslim sect in the mountains of Lebanon at the time of the Crusades, under leadership of the "Old Man of the Mountains" (which translates Arabic shaik-al-jibal, name applied to Hasan ibu-al-Sabbah). In Western European minds 12c.-13c. they had a reputation for murdering opposing leaders after intoxicating themselves by eating hashish, but there is no evidence that the medieval Ismailis used hashish.
The plural suffix -in was mistaken in Europe for part of the word (compare Bedouin). Middle English had the word as hassais (mid-14c.), from Old French hassasis, assasis, which is from the Arabic word.
The generalization of the sect's nickname to the meaning of any sort of assassin happened in Italian at the start of the 14th century. The word with the generalized meaning was often used in Italian in the 14th and 15th centuries. In the mid 16th century the generalized Italian word entered French, followed a little later by English. ["English Words of Arabic Ancestry"]
1830, "a decisive blow" (also, figuratively "a conclusive argument"), fanciful formation from sock (v.1) "hit hard," perhaps via a comical mangling of doxology, on a notion of "finality." The meaning "something exceptional" is attested from 1838.
Sockdologizing likely was nearly the last word President Abraham Lincoln heard. During the performance of Tom Taylor's "Our American Cousin," assassin John Wilkes Booth (who knew the play well) waited for the laugh-line:
Don't know the manners of good society, eh? Well, I guess I know enough to turn you inside out, old gal—you sockdologizing old man-trap.
Amid the noise as the audience responded, Booth fired the fatal shot.
"low-waisted two-piece women's bathing suit," 1948, from French, coined 1947, named for the U.S. A-bomb test of June 1946 on Bikini, the Marshall Islands atoll, locally Pikinni and said to derive from pik "surface" and ni "coconut," but this is uncertain. Various explanations for the swimsuit name have been suggested, none convincingly, the best being an analogy of the explosive force of the bomb and the impact of the bathing suit style on men's libidos (compare c. 1900 British slang assassin "an ornamental bow worn on the female breast," so called because it was very "killing," also the figurative sense of bombshell).
Bikini, ce mot cinglant comme l'explosion même ... correspondant au niveau du vêtement de plage à on anéantissement de la surface vêtue; à une minimisation extrême de la pudeur. [Le Monde Illustré, August 1947]
As a style of scanty briefs, from 1960. Variant trikini (1967), with separate bra cups held on by Velcro, falsely presumes a compound in bi-.
c. 1300 (mid-12c. in surnames), "small axe with a short handle," designed to be used by one hand, from Old French hachete "small combat-axe, hatchet," diminutive of hache "axe, battle-axe, pickaxe," possibly from Frankish *happja or some other Germanic source, from Proto-Germanic *hapjo- (source also of Old High German happa "sickle, scythe").
This is perhaps from PIE root *kop- "to beat, strike" (source also of Greek kopis "knife," koptein "to strike, smite," komma "piece cut off;" Lithuanian kaplys "hatchet," kapti, kapiu "to hew, fell;" Old Church Slavonic skopiti "castrate," Russian kopat' "to hack, hew, dig;" Albanian kep "to hew").
Hatchet-face in reference to one with sharp and prominent features is from 1650s. In Middle English, hatch itself was used in a sense "battle-axe." In 14c., hang up (one's) hatchet meant "stop what one is doing." Phrase bury the hatchet "lay aside instruments of war, forget injuries and make peace" (1754) is from a Native American peacemaking custom described from 1680. Hatchet-man was originally California slang for "hired Chinese assassin" (1880), later extended figuratively to journalists who attacked the reputation of a public figure (1944).