Kaʻahumanu (Hawaiian, ka ʻahu manu, "the feather cloak") was the favorite wife of King Kamehameha I — the unifier of the Hawaiian Islands — and queen-regent (kuhina nui) of the Kingdom of Hawaii from 1819 to 1832.
Kaahumanu 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 Kaahumanu reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.