1550s, "disbelieve, give no credit to," from dis- "opposite of" + credit (v.). Meaning "show to be unworthy of belief" is from 1560s; that of "injure the reputation of, make less esteemed or honored" is from 1570s. As a noun, "want of credit or good repute," 1560s, from the verb. Related: Discredited; discrediting.
1550s, "disfigure, deprive of (outward) grace," a sense now obsolete; 1590s, "put out of favor, dismiss with discredit," also "bring shame or reproach upon" from French disgracier (16c.), from Italian disgraziare, from disgrazia "misfortune, deformity," from dis- "opposite of" (see dis-) + grazia "grace" (see grace (n.)). Related: Disgraced; disgracing.
mid-15c., "make an initial statement setting out a plaintiff's case," from libel (n.), which see for sense development. Meaning "defame or discredit by libelous statements" is from c. 1600. Related: Libeled; libelled; libeling; libelling; libellant; libellee.
c. 1600, "assault, assail, begin hostilities against," from French attaquer (16c.), from Florentine Italian attaccare (battaglia) "join (battle)," thus the word is a doublet of attach, which was used 15c.-17c. also in the sense now reserved to attack.
The meaning "endeavor to bring into discredit by writing, proposals, etc." is from 1640s. The general sense of "begin action" is from 1670s, originally of diseases. Related: Attacked; attacking.
late 15c., smorchen, "to discolor, to make dirty" (also compare bismorched, mid-15c.), a word of uncertain origin, perhaps (OED) from Old French esmorcher "to torture," which is perhaps also "befoul, stain," from es- "out" (see ex-) + morcher "to bite," from Latin morsus, past participle of mordēre "to bite" (see mordant). The sense perhaps was influenced by smear. The figurative meaning "dishonor, disgrace, discredit" is attested from 1820.
"to discredit a candidate for some position by savaging his or her career and beliefs," 1987, from name of U.S. jurist Robert H. Bork (1927-2012), whose Supreme Court nomination in 1987 was rejected after an intense counter-campaign. Not the first name to be so used:
[John Quincy Adams's] printed assault upon Jonathan Russell—who had been so ill-advised as to cast doubts upon the patriotism of Adams's conduct at Ghent—was so deadly that for many years afterwards the vocabulary of America was increased, though not enriched, by the transitive verb "to Jonathan-Russell," meaning to pulverize an opponent. [George Dangerfield, "The Era of Good Feeling," 1953]
1580s, "damage to one's reputation," from French scandale, from Late Latin scandalum "cause for offense, stumbling block, temptation," from Greek skandalon "a stumbling block, offense; a trap or snare laid for an enemy."
The Greek noun in this form seems to be attested first in Septuagint (25 times) and the Greek New Testament (15 times) as "cause of moral stumblings," translating a Hebrew word meaning "a noose, a snare." The Biblical use is presumably figurative or metaphoric, and OED and others conclude that it is "certainly an old word meaning 'trap' " or a variant of one. Presumably, then, originally "trap with a springing device" (compare related skandalē "stick of a trap," the trigger which is pulled by the cord to spring it), if it is from PIE *skand- "to leap, climb" (see scan (v.), as is proposed in Watkins (Beekes is skeptical); also see slander (n.), which is another form of the same word.
The word is used in "Ancrene Riwle" (c. 1200), scandle, "discredit to religion resulting from bad behavior by a religious person," from Old French escandle, eschandle (12c.); Anglo-French scandle, and Latin scandalum. But the modern word likely is a new borrowing.
The meanings "malicious gossip" and "shameful condition, action, or event; that which causes scandal" are from 1590s; the sense of "person whose conduct is a disgrace" is by 1630s. Scandal sheet "sensational newspaper" is by 1884. Scandal-monger is from 1702.
late 13c., sclaundre, "state of impaired reputation; disgrace or dishonor;" c. 1300, "a false tale or report spread maliciously; the fabrication and dissemination of false tales to discredit someone," from Anglo-French esclaundre, Old French esclandre "scandalous statement," alteration ("with interloping l" [Century Dictionary]) of escandle, escandre "scandal," from Latin scandalum "cause of offense, stumbling block, temptation" (see scandal).
It is attested from mid-14c. as "action or situation that brings shame or disgrace;" late 14c. as "a bad situation, evil action" and in reference to a person causing such a state of affairs.
The injury [slander] consists in falsely and maliciously charging another with the commission of some public offense criminal in itself, and indictable, and subjecting the party to an infamous punishment, or involving moral turpitude, or the breach of some public trust, or with any matter in relation to his particular trade or vocation, and which, if true, would render him unworthy of employment ; or, lastly, with any other matter or thing by which special injury is sustained. [James Kent, "Commentaries on American Law," 1844]
also gas-light, "light, or a provision for light, produced by combustion of coal gas; a gas-jet," 1808, from (illuminating) gas (n.1) + light (n.). Used through the 19th and into the early 20th century as street and domestic lighting. Related: Gas-lighted; gas-lighting; gaslighting.
As a verb meaning "to deliberately make a person believe that they are insane," by 1961, perhaps 1956. This sense is from the 1944 film Gaslight, in which a 19th century woman (played by Ingrid Bergman, who won an Academy Award) appears to be going mad. It is later revealed that her criminal husband has been convincing her that she is insane in order to discredit her observations of his activities. Among the observable clues has been the dimming of their home's gaslighting whenever (as she later learns) the husband goes secretly into the attic: he has convinced her that she is imagining this, until a family friend sees it, too, which confirms the clue that uncovers the crime.
Brian: Tell me. Is there anyone else in the house now, except us and Elizabeth?
Paula: No. Why?
Brian: The gas just went down.
Paula: You saw that too!
Brian: Why, yes.
Paula: Oh, then it really happens! I thought I imagined it!
Brian: But all it means is someone else has turned it on.
Paula: Oh, no, no. I thought that too. But every night, I’ve been all over the house, there’s never been another light turned on. At last I can tell this to someone! Every night when my husband goes out…
Brian: …The light goes down?
Brian: And then what?
Paula: Well, then, I think I hear things. I watch and wait. Later on, the gas goes up again.
Brian: And he comes back?
Paula: Yes. Quite soon after. Always quite soon after.
The word seems to have received a boost in feminist literature in late 1970s.
… I had been told that my tonsillectomy was “not that bad” or that the dentist whose hands were between my legs was “fixing my teeth,” … My own favorite embodiment of this horror, still enjoyed by late-show insomniacs, is the 1944 film Gaslight, a tale which so impressed the public imagination that even today the word “gaslight” is used to describe an attempt to destroy another’s perceptions of reality and, ultimately, sanity itself. [Florence Rush, "The Best Kept Secret: Sexual Abuse of Children," 1980]
The sense evolved by 2016 to also mean "dismiss or discredit someone's viewpoint."