Alda means a wave, a swell of the sea — and also an age or era. It carries motion, depth and time.
Alda 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 Alda reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.