Bellatrix comes from the Latin bellatrix, meaning "female warrior" — the feminine of bellator. The name is also that of the third-brightest star in the constellation Orion (the Amazon Star).
Bellatrix is rising as a girls' name despite its association with the Harry Potter villain Bellatrix Lestrange — parents drawn to the star and the warrior meaning.
Bellatrix 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 Bellatrix reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.