Fionnuala combines the Irish fionn (fair, white) and guala (shoulder) — meaning "fair-shouldered." In Irish legend, Fionnuala is the daughter of Lir who was transformed with her brothers into swans for 900 years.
Fionnuala is widely used in Ireland.
Fionnuala 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 Fionnuala reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.