Etymology
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misadventure (n.)

"an unfortunate experience, a bad experience, ill-luck, calamity," c. 1300, misaventure, from Old French mesaventure (12c.) "accident, mishap," from mesavenir "to turn out badly;" see mis- (2) + adventure (n.) in the older sense of "that which happens by chance, fortune, luck." The spelling with -d- became regular after c. 1600.

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mis- (2)

word-forming element of Latin origin (in mischief, miscreant, misadventure, misnomer, etc.), from Old French mes- "bad, badly, wrong, wrongly," from Vulgar Latin *minus-, from Latin minus "less" (from suffixed form of PIE root *mei- (2) "small"), which was not used as a prefix in Latin but in the Romanic languages was affixed to words as a depreciative or negative element. The form in French perhaps was influenced in Old French by *miss-, the Frankish (Germanic) form of mis- (1).

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*gwa- 

*gwā-, also *gwem-, Proto-Indo-European root meaning "to go, come."

It forms all or part of: acrobat; adiabatic; advent; adventitious; adventure; amphisbaena; anabasis; avenue; base (n.) "bottom of anything;" basis; become; circumvent; come; contravene; convene; convenient; convent; conventicle; convention; coven; covenant; diabetes; ecbatic; event; eventual; hyperbaton; hypnobate; intervene; intervenient; intervention; invent; invention; inventory; juggernaut; katabatic; misadventure; parvenu; prevenient; prevent; provenance; provenience; revenant; revenue; souvenir; subvention; supervene; venire; venue; welcome.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gamati "he goes," Avestan jamaiti "goes," Tocharian kakmu "come," Lithuanian gemu, gimti "to be born," Greek bainein "to go, walk, step," Latin venire "to come," Old English cuman "come, approach," German kommen, Gothic qiman.

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manslaughter (n.)

early 14c., " act, crime, or sin of killing another human being," in battle or not, from man (n.) + slaughter (n.). It gradually displaced manslaught, the earlier word, from Old English manslæht (Anglian), manslieht (West Saxon), from slæht, slieht "act of killing" (see slay (v.)). Middle English also had man-quelling "murder, homicide" (late 14c.), and slaughter-man (late 14c.), "an executioner; a butcher."

Etymologically it is comparable to Latin homicide, but in legal use usually it is distinguished from murder and restricted to "simple homicide, unlawful killing of another without malice either express or implied."

Manslaughter differs from murder in not proceeding from malice prepense or deliberate, which is essential to constitute murder. It differs from excusable homicide, being done in consequence of some unlawful act, whereas excusable homicide happens in consequence of misadventure. Manslaughter has been distinguished as voluntary, where the killing was intentional in a sudden heat or passion without previous malice; and involuntary, where it was not intentional, but the slayer was at the time engaged in an unlawful act less than a felony, or doing a lawful act in an unlawful manner. [Century Dictionary]
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