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. My bad as an acknowledgement of a mistake is by 1995.

Ironic use of bad as a word of approval is said to be at least since 1890s orally, originally in African-American vernacular; it is in print by 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"]

[N.B.] 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."

also evil-doer, "one who does evil, one who commits moral wrong," late 14c., from evil (n.) + doer.

c. 1200, "morally evil; offensive, objectionable" (other 13c. senses were "malevolent, hurtful, unfortunate, difficult"), from Old Norse illr "evil, bad; hard, difficult; mean, stingy," a word of unknown origin. Not considered to be related to evil. From mid-14c. as "marked by evil intentions; harmful, pernicious." Sense of "sick, unhealthy, diseased, unwell" is first recorded mid-15c., probably from a use similar to that in the Old Norse idiom "it is bad to me." Slang inverted sense of "very good, cool" is 1980s.

comparative adjective, "more unfortunate or undesirable," also in reference to health, wealth, etc., Middle English werse, from Old English wiersa, wyrsa "more evil, culpable, sinful, unpleasant," etc., from Proto-Germanic *wers-izon-.

This is reconstructed (Watkins) to be comparative of PIE *wers- (1) "to confuse, mix up" (source also of Old High German werra "strife," Old Saxon werran "to entangle, compound;" see war (n.)).

Also used as a comparative of bad, evil, ill or as the opposite of better. Of things, "in less good condition, less valuable or perfect," by c. 1200.

The comparative adverb, "more evilly, in a way less good or desirable," is Old English wyrs. Also see worse (n.). Germanic cognates include Old Norse verri, Swedish värre, Old Frisian wirra, Old High German wirsiro, Gothic wairsiza "worse."