quintile (n.)

1610s, originally in astrology and said to have been introduced by Kepler, "aspect of planets when they are 72 degrees from each other" (a fifth of the zodiac), from Latin quintus "the fifth" (from PIE root *penkwe- "five") + ending from quartile. Its use in statistics in reference to a division data points into five parts of more or less equal size dates to 1951.

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