The story
Origin uncertain, first recorded in the mid 16th century, probably related to Latin flagrō (“to 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. The noun is derived from the verb.
Etymology from Wiktionary, CC BY-SA 4.0.