Penthesilea (Πενθεσίλεια) combines the Greek penthos (grief) and laos (people) — meaning "mourning of the people." The Amazon queen who fought alongside the Trojans and was killed in single combat by Achilles, who fell in love with her at the moment of her death.
Penthesilea is rare but iconic.
Penthesilea 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 Penthesilea reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.