1835, "inflict severe (but not deliberately fatal) bodily punishment (on someone) without legal sanction," from earlier Lynch law (1811), in reference to such activity, which was likely named after William Lynch (1742-1820) of Pittsylvania, Virginia, who c. 1780 led a vigilance committee to keep order there during the Revolution. Other sources trace the name to Charles Lynch (1736-1796) a Virginia magistrate who fined and imprisoned Tories in his district c. 1782, but the connection to him is less likely. The surname is perhaps from Irish Loingseach "sailor."

It implies lawless concert or action among a number of members of the community, to supply the want of criminal justice or to anticipate its delays, or to inflict a penalty demanded by public opinion, though in defiance of the laws. [Century Dictionary, 1895]

Originally any sort of summary justice, done without authority of law, for a crime or public offense; it especially referred to flogging or tarring-and-feathering. At first the act was associated with frontier regions (as in the above citation), though from c. 1835 to the U.S. Civil War it also often was directed against abolitionists. The narrowing of the meaning to "extra-legal execution by hanging" is evident by the 1880s, and after c. 1893 lynching mostly meant killings of blacks by white mobs (especially in retaliation for alleged sexual assaults of white women). This shift in use seems due in part to the work of African-American journalist and activist Ida B. Wells. Lynch mob is attested from 1838.

Compare earlier Lydford law, from the place in Devon, a seat of the old notorious Stannaries Courts, "that hanged a man in the forenoone, and sate in judgment on him in the afternoone" (1633 description; see stannary).

Also in a similar sense was Jedburgh justice (1706) in reference to the town on the volatile Scottish borders, and, as a verb, to Dewitt (1680s), a reference to two Dutch statesmen of that name, opponents of William of Orange, murdered by a mob in 1672.

Related: Lynched; lynching. The city of Lynchburg, Virginia, dates to the 1750s when John Lynch, brother to Charles but a peaceable Quaker, had a ferry landing on the James River there.

1836, verbal noun from lynch (v.).

also scallawag, "disreputable fellow," by 1839, American English colloquial, of uncertain origin; perhaps an alteration (by influence of wag "habitual joker") of Scottish scallag "farm servant, rustic," itself an alteration of Scalloway, one of the Shetland Islands, the reference being to little Shetland ponies (an early recorded sense of scalawag was "undersized, ill-fed, or worthless animal," 1854).

Judge Lynch passed through town on Saturday night last. He remained here long enough to give a worthless scalawag a genteel suit, from "head to heels" of tar and feathers. [Maumee City Express, Saturday Aug. 3, 1839]

In U.S. history, used from 1862 as a derogatory term for anti-Confederate native white Southerners.

The word was used in the southern United States, during the period of reconstruction (1865 to 1870 and later), in an almost specific sense, being opprobriously applied by the opponents of the Republican party to native Southerners who acted with that party, as distinguished from carpet-bagger, a Republican of Northern origin. [Century Dictionary]