Themistoclea (Θεμιστόκλεια, 6th c. BCE) was the priestess of Apollo at Delphi who taught Pythagoras his moral doctrines — making her the earliest known female philosopher and one of the figures of Western thought.
Mentioned in Diogenes Laërtius and Porphyry of Tyre.
Themistoclea 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.
In Pythagorean numerology the letters of Themistoclea reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.