"broad diagonal band in a coat-of-arms, etc.," mid-14c., from the earlier sense of "thin, flat strap for wrapping round," from Old English bend "fetter, shackle, chain," from PIE *bhendh- "to bind" (see bend (v.)). Probably in part also from Old French bende (Modern French bande) and Medieval Latin benda, both of them from Germanic. Ordinarily running from the right top to the left bottom; the bend sinister runs along the other diagonal.
late 14c., "not in conformity with Church rules," from Old French irreguler "irregular, incapable, incompetent" (13c., Modern French irrégulier), from Medieval Latin irregularis "not regular," from assimilated form of in- "not, opposite of" (see in- (1)) + Latin regularis "having rules" (see regular (adj.)). General sense of "not conforming to regular rules or principles" is from late 15c. "It expresses the fact of being out of conformity with rule, but implies nothing more with certainty. Yet the word is sometimes used in a sinister sense, as though it were a euphemism for something worse." [Century Dictionary] Meaning "unsymmetrical" is from 1580s. In reference to variable stars, from 1797.
in the figurative sense "wildly irresponsible person, potent person or thing freed from usual restraint," by 1896; in the literal sense an object of dread on old warships; the figurative use probably arose from a celebrated scene in a popular late novel by Victor Hugo:
You can reason with a bull dog, astonish a bull, fascinate a boa, frighten a tiger, soften a lion; no resource with such a monster as a loose cannon. You cannot kill it, it is dead; and at the same time it lives. It lives with a sinister life which comes from the infinite. It is moved by the ship, which is moved by the sea, which is moved by the wind. This exterminator is a plaything. [Victor Hugo, "Ninety Three," 1874]
Middle English derk, later dark, from Old English deorc "without light, lacking light or brightness (especially at night), obscure, gloomy;" figuratively "sad, cheerless; sinister, wicked," from Proto-Germanic *derkaz (source also of Old High German tarchanjan "to hide, conceal"), which is of uncertain etymology. For vowel change, see marsh.
Application to colors, "not radiating or reflecting much light," is from late 14c. Of complexion, "not fair," from early 14c. Figurative sense of "obscure, not easily understood" is from early 13c.; that of "sullen, sad" is from 1590s. Meaning "concealed, secret" is from late 14c. Dark Continent "Africa" (1828) combines several figurative senses (earliest references are in missionary publications). Theater slang for "closed" is from 1916.
Dark Ages "benighted time in history, period of ignorance" is attested by 1739; the specific focus on the centuries of the early Middle Ages in Europe, from the fall of Rome to the revival of secular literature, is from 1830s, from dark in a sense of "characterized by ignorance, backward in learning, void of intellectual light" (late 14c.).
Dark horse "competitor for honors or office about whom nothing certain is known, or whose identity is at first concealed," especially, in U.S., politics, "one who is unexpectedly brought forward as a candidate in a convention," 1842, is an image from horse racing, of horses whose performances or capabilities are not generally known, in which dark is used in its figurative sense of "unknown."
Moonraker is called a "dark horse"; that is neither his sire nor dam is known. ["Pierce Egan's Book of Sports," London, 1832]
c. 1300, "inadequate, unsatisfactory, worthless; unfortunate;" late 14c., "wicked, evil, vicious; counterfeit;" from 13c. in surnames (William Badde, Petri Badde, Asketinus Baddecheese, Rads Badinteheved). Rare before 1400, and evil was more common until c. 1700 as the ordinary antithesis of good. It has no apparent relatives in other languages.* It is possibly from Old English derogatory term bæddel and its diminutive bædling "effeminate man, hermaphrodite, pederast," which probably are related to bædan "to defile."
The orig. word, AS. bæddel, ME. baddel, on account of its sinister import, is scarcely found in literature, but, like other words of similar sense, it prob. flourished in vulgar speech as an indefinite term of abuse, and at length, divested of its original meaning, emerged in literary use as a mere adj., badde, equiv. to the older evil. [Century Dictionary, 1897]
Comparable words in the other Indo-European languages tend to have grown from descriptions of specific qualities, such as "ugly," "defective," "weak," "faithless," "impudent," "crooked," "filthy" (such as Greek kakos, probably from the word for "excrement;" Russian plochoj, related to Old Church Slavonic plachu "wavering, timid;" Persian gast, Old Persian gasta-, related to gand "stench;" German schlecht, originally "level, straight, smooth," whence "simple, ordinary," then "bad").
Comparative and superlative forms badder, baddest were common 14c.-18c. and used as recently as Defoe (but not by Shakespeare), but yielded to comparative worse and superlative worst (which had belonged to evil and ill).
The meaning "uncomfortable, sorry" is 1839, American English colloquial. To go bad "putrefy" is from 1884. Not bad "fairly good" is by 1771. Ironic use as a word of approval is said to be at least since 1890s orally, originally in African-American vernacular, emerging in print 1928 in a jazz context. It might have emerged from the ambivalence of expressions like bad nigger, used as a term of reproach by whites, but among blacks sometimes representing one who stood up to injustice. In the U.S. West bad man also had a certain ambivalence:
These are the men who do most of the killing in frontier communities, yet it is a noteworthy fact that the men who are killed generally deserve their fate. [Farmer and Henley, "Slang and Its Analogues"]
*Persian has bad in more or less the same sense as the English word, but this is regarded by linguists as a coincidence. The forms of the words diverge as they are traced back in time (Persian bad comes from Middle Persian vat), and such accidental convergences exist across many languages, given the vast number of words in each and the limited range of sounds humans can make to signify them. Among other coincidental matches with English are Korean mani "many," Chinese pei "pay," Nahuatl (Aztecan) huel "well," Maya hol "hole."