Ju means the chrysanthemum — the flower of autumn, longevity and quiet nobility. It carries endurance and grace.
Ju does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Ju reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.