Grows or develops in a healthy way; also decorative curves or embellishments added for style.
From Old French 'florir' meaning to bloom or flower, derived from Latin 'florere' (to flower). The noun sense developed from the visual appearance of flowery decorations, while the verb kept the sense of thriving like a flower.
Medieval monks created elaborate 'flourishes' in manuscripts—fancy scrollwork in margins—and the word is perfect because they look like flowers blooming on the page, the same word describing both healthy growth and beautiful decoration.
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