Sini is the Finnish word for "blue" — short for Sinikka (meaning "like the blueness"). Evokes the Finnish lakes and sky.
Sini is widely used in Finland.
Sini 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 Sini reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.