Etymology
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bacon (n.)

early 14c., "meat from the back and sides of a hog" (originally either fresh or cured, but especially cured), from Old French bacon, from Proto-Germanic *bakkon "back meat" (source also of Old High German bahho, Old Dutch baken "bacon"), from the source of back (n.).

The slang phrase bring home the bacon "succeed in supplying material provisions to support a standard of living," also figurative, is recorded by 1906, originally perhaps in pugilism slang. Bacon formerly was the staple meat of the working class and the rural population (in Shakespeare bacon is a derisive term for "a rustic").

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bacteria (n.)

"unicellular microorganisms which lack an organized nucleus," and sometimes cause disease, 1847, plural of Modern Latin bacterium, from Greek bakterion "small staff," diminutive of baktron "stick, rod, staff, cudgel." So called because the first ones observed were rod-shaped. Introduced as a scientific word 1838 by German naturalist Christian Gottfried Ehrenberg. A classical plural sometimes also erroneously used as a singular.

The Greek word is from a PIE *bak- "staff used for support, peg" (compare Latin baculum "rod, walking stick;" Irish bacc, Welsh bach "hook, crooked staff;" Middle Dutch pegel "peg, pin, bolt"). De Vaan writes, "Since *b was very rare in PIE, and Celtic shows an unexplained geminate, we are probably dealing with a loanword from an unidentified source."

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bacterial (adj.)

"of or pertaining to bacteria," 1869, from bacteria + -al (1).

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bacteriology (n.)

"scientific study of microbes," 1884, from German; see bacteria + -ology. Related: Bacteriological (1886); bacteriologist. Bacteriological warfare is attested from 1924.

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bacteriophage (n.)

"virus that parasitizes a bacterium by infecting it and reproducing inside it," 1921, from French bactériophage (1917), from bacterio-, combining form of bacteria, + -phage.

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Bactrian (n.)

late 14c., "inhabitant of Bactria," ancient region in what is now northwestern Afghanistan; as a type of camel c. 1600; from Latin Bactria, from Persian, literally "the western province," from bakhtar "the west."

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bad (n.)

late 14c., "evil, wickedness," from bad (adj.).

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bad (adj.)

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."

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bad-ass (n.)

also badass, "tough guy," 1950s U.S. slang, from bad (adj.) + ass (n.2).

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