A sudden bright light or fire that shoots upward; also means a widening shape, like bell-bottom pants.
From Old Norse 'flærra' meaning to spread out. Originally described the widening motion, then applied to sudden bright lights that spread outward and upward.
A flare-up in astronomy is when a star suddenly brightens, and a flare-up in conflict is when fighting suddenly intensifies—the word describes any moment when something suddenly becomes bigger, brighter, or more intense. It's physics and human nature described with one word.
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