flagrant: [15] Etymologically, flagrant means ‘burning, blazing’. It comes, via French, from the present participle of Latin flagrāre ‘burn’ (source of English conflagration [16]). This in turn went back to Indo-European *bhleg-, which also produced English flame. The use of flagrant for ‘shameless, shocking’, an 18th-century development, comes from the Latin phrase in flagrante delicto ‘red-handed’, literally ‘with the crime still blazing’. => conflagration, flame
flagrant (adj.)
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" (cognates: Oscan flagio-, an epithet of Iuppiter), corresponding to PIE *bhleg-ro-, from *bhleg- "to shine, flash, burn" (cognates: Greek phlegein "to burn, scorch," Latin fulgere "to shine"), from root *bhel- (1) "to shine, flash, burn" (see bleach (v.)). 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.