flare (v.) Look up flare at Dictionary.com
mid-16c., originally "spread out" (hair), of unknown origin, perhaps from Dutch vlederen. Related: Flared; flaring. The notion of "spreading out in display" is behind the notion of "spreading gradually outward" (1640s). Flare-up "a sudden burst" is from 1837.
flare (n.) Look up flare at Dictionary.com
"bright, unsteady light," 1814, from flare (v.), which led to the sense of "signal fire" (1883). Flares "flared trousers" is from 1964.