c. 1500, "resplendent" (obsolete), from Latin flagrantem (nominative flagrans) "burning, blazing, glowing," figuratively "glowing with passion, eager, vehement," present participle of flagrare "to burn, blaze, glow," from Proto-Italic *flagro- "burning" (source also of Oscan flagio-, an epithet of Iuppiter), corresponding to PIE *bhleg-ro-, from *bhleg- "to shine, flash, burn" (source also of Greek phlegein "to burn, scorch," Latin fulgere "to shine"), from root *bhel- (1) "to shine, flash, burn." Sense of "glaringly offensive, scandalous" (rarely used of persons) first recorded 1706, probably from common legalese phrase flagrante delicto "while the crime is being committed, red-handed," literally "with the crime still blazing." Related: Flagrantly.
Proto-Indo-European root meaning "to shine, flash, burn," also "shining white" and forming words for bright colors.
It forms all or part of: beluga; Beltane; black; blancmange; blanch; blank; blanket; blaze (n.1) "bright flame, fire;" bleach; bleak; blemish; blench; blende; blend; blind; blindfold; blitzkrieg; blond; blue (adj.1); blush; conflagration; deflagration; effulgence; effulgent; flagrant; flambe; flambeau; flamboyant; flame; flamingo; flammable; Flavian; Flavius; fulgent; fulminate; inflame; inflammable; phlegm; phlegmatic; phlogiston; phlox; purblind; refulgent; riboflavin.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhrajate "shines;" Greek phlegein "to burn;" Latin flamma "flame," fulmen "lightning," fulgere "to shine, flash," flagrare "to burn, blaze, glow;" Old Church Slavonic belu "white;" Lithuanian balnas "pale."
"a transgression or offense," in civil law, a misdemeanor, 1520s, from Latin delictum "fault, offense, crime," neuter singular of past participle of delinquere "to fail; be wanting, fall short; offend," from de- "completely" (see de-) + linquere "to leave" (from PIE root *leikw- "to leave"). Related: Delictable "criminal, wicked," early 15c. Phrase in flagrant delict translates Latin in flagrante delicto.
Delicts are commonly understood as slighter offenses which do not immediately affect the public peace, but which imply an obligation on the part of the offender to make an atonement to the public by suffering punishment, and also to make reparation for the injury committed The term delinquency has the same signification. [Century Dictionary]
Its meaning forked in English. Via the notion of "coarse in texture or quality" came the senses "not sensitive, dull stupid" (1520s), "vulgar, coarse in a moral sense" (1530s). Via notion of "general, not in detail" came the sense "entire, total, whole, without deductions" (early 15c.), as in gross national product (1947). Meaning "glaring, flagrant, monstrous" is from 1580s; modern meaning "disgusting" is first recorded 1958 in U.S. student slang, from earlier use as an intensifier of unpleasant things (gross stupidity, etc.).