Sothea (សុធា) means "perfect" or "accomplished" in Khmer — also borrowed from the Sanskrit sudhā (nectar, ambrosia). A traditional Cambodian feminine name.
Used widely in modern Cambodia.
Sothea 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 Sothea reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.