Arabella is from the Latin orabilis ("yielding to prayer, entreatable") — also interpreted as the Italian ara bella ("beautiful altar"). A top-200 US baby name since 2010. Arabella Weir — Scottish actress and comedian. Western's niece Arabella Hunt.
Arabella 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 Arabella reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.