mid-14c., from Anglo-French flaume, Old French flamme (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" (see bleach (v.)).
The meaning "a sweetheart" is attested from 1640s; the figurative sense of "burning passion" was in Middle English. Flame-thrower (1917) translates German flammenwerfer (1915).
The hot, glowing mixture of burning gases and tiny particles that arises from combustion. Flames get their light either from the fluorescence of molecules or ions that have become excited, or from the incandescence of solid particles involved in the combustion process, such as the carbon particles from a candle.