Blathnaid is from the Old Irish Bláthnait — bláth (flower) + -nait (diminutive) — little flower. Bláthnait in Irish mythology is the princess and wife of Cú Roí mac Dáire — central to the Ulster Cycle alongside Queen Medb (Meadhbh) and Cú Chulainn. Her tragic tale — kidnapped from her father, forced into marriage with Cú Roí, then betrays him to her lover Cú Chulainn, only to be killed in revenge by Cú Roí's poet Ferchertne — is one of the tragic love stories of Old Irish literature. Irish-language feminine name in modern Gaeltacht communities.
Blathnaid 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.
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In Pythagorean numerology the letters of Blathnaid reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.