Sen means the lotus — the flower that rises clean from the water, beloved in Vietnam. It carries purity and serene beauty.
Sen 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 Sen reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.