"a setting on fire," c. 1600, from Latin deflagrationem (nominative deflagratio) "a burning up, conflagration," noun of action from past-participle stem of deflagrare, from de (see de-) + flagrare "to burn, blaze, glow," from PIE root *bhel- (1) "to shine, flash, burn." Related: Deflagrate, deflagrating.
1650s, "to catch fire," from Latin conflagratus, past participle of conflagrare "to burn, consume," from assimilated form of com-, here perhaps an intensive prefix (see con-), + flagrare "to burn, blaze, glow" (from PIE root *bhel- (1) "to shine, flash, burn"). Transitive meaning "to set on fire" is from 1835.
c. 1600, "to expose to moonlight;" later "idle about, wander or gaze moodily" (1836), "move listlessly" (1848), probably on the notion also found in moonstruck. The meaning "to flash the buttocks" is recorded by 1968, U.S. student slang, from moon (n.) "buttocks" (1756), "probably from the idea of pale circularity" [Ayto]. See moon (n.). Related: Mooned; mooning.
1590s, from Russian beluga, literally "great white," from belo- "white" (from PIE *bhel-o-, suffixed form of root *bhel- (1) "to shine, flash, burn," also "shining white") + augmentative suffix -uga. Originally the great white sturgeon, found in the Caspian and Black seas; later (1817) the popular name for the small white whale (Delphinapterus leucas) found in northern seas.
Middle English flaume, also flaumbe, flambe, flame, flamme, mid-14c., "a flame;" late 14c., "a flaming mass, a fire; fire in general, fire as an element;" also figurative, in reference to the "heat" or "fire" of emotions, from Anglo-French flaume, flaumbe "a flame" (Old French flambe, 10c.), from Latin flammula "small flame," diminutive of flamma "flame, blazing fire," from PIE *bhleg- "to shine, flash," from root *bhel- (1) "to shine, flash, burn."
The meaning "a sweetheart, object of one's passion" is attested from 1640s; the figurative sense of "burning passion" was in Middle English, and the nouns in Old French and Latin also meant "fire of love, flame of passion," and, in Latin "beloved object." The Australian flame-tree is from 1857, so called for its red flowers.
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."
"shrink, start back, give way; flinch, wince, dodge," c. 1200, an extended sense from Old English blencan "deceive, cheat" (obsolete in the original sense), from Proto-Germanic *blenk- "to shine, dazzle, blind" (source also of Old Norse blekkja "delude"), from PIE root *bhel- (1) "to shine, flash, burn," also "shining white." Related: Blenched; blenching.
1550s, "a destructive fire;" 1650s, "a large fire, the burning of a large mass of combustibles," from French conflagration (16c.) or directly from Latin conflagrationem (nominative conflagratio), noun of action from past-participle stem of conflagrare "to burn up," from assimilated form of com-, here perhaps an intensive prefix (see con-), + flagrare "to burn, blaze, glow" (from PIE root *bhel- (1) "to shine, flash, burn").