Hien is from the Vietnamese Hiền (gentle, virtuous, kind). Hien is one of the Vietnamese feminine names expressing the Confucian virtue of hiền — central to traditional Vietnamese (and East Asian) moral philosophy alongside nhân (humaneness), trí (wisdom), and dũng (courage). The Vietnamese feminine ideal of hiền lành (gentle and kind) is one of the cultural virtues celebrated in Vietnamese literature and family naming.
Hien 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 Hien reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.