From Latin 'flamma' (fire), from PIE *bhleg- (to shine, burn) — same root behind flamingo and flagrant.
A hot glowing body of ignited gas.
From Old French 'flamme,' from Latin 'flamma' (flame), from PIE *bhleg- (to shine, burn). Same root gives 'flagrant' and 'flamingo.' Key roots: *bhleg- (PIE: "to shine, burn").