Una has two parallel origins. In Latin, una means "one" — used as a name meaning "unity" or "the one." In Irish, Úna comes from uan, meaning "lamb." The two etymologies converge on a short, gentle name.
The name has been continuously used in Ireland and parts of Scandinavia. Today it sits outside the U.S. top 1000 but is rising slowly.
Una 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 Una reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.