Flare
mid 16th century (in the sense ‘spread out one's hair’): of unknown origin. Current senses date from the 17th century.
wiktionary
Origin unknown, first recorded in the mid 16th century, probably related to Latin flagrō(“I burn”). Norwegian flara(“to blaze; to flaunt in gaudy attire”) has a similar meaning, but the English word predates it. Possibly related to Middle High German vlederen(“to flutter”), represented by modern German flattern. [1]
The noun is derived from the verb. [2]
etymonline
flare (v.)
1540s, "spread out" (hair), of unknown origin, perhaps from Scandinavian or from Dutch vlederen. Meaning "shine out with a sudden light" is from 1630s. The notion of "spreading out in display" is behind the notion of "spreading gradually outward" (1640s). Related: Flared; flaring.
flare (n.)
"a giving off of a bright, unsteady light," 1814, from flare (v.). This led to the sense of "signal fire" (1883). The astronomy sense is from 1937. Meaning "a gradual widening or spreading" is from 1910; hence flares "flared trousers" (1964).
