Volumnia is from the Latin volumen (roll, volume). Volumnia (5th c. BCE) was the wife of Coriolanus — featured alongside his mother in the embassy that saved Rome.
Volumnia 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 Volumnia reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.