Nirosha is from the Sinhala / Sanskrit Nirosha (නිරෝෂා — nir- without + rosha anger / roś light) — without anger or eternally brilliant. Nirosha is one of the Sinhala feminine names — central to traditional Sri Lankan Theravada Buddhist heritage.
Nirosha 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 Nirosha reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.