Ianthe means violet flower, from ion (violet) and anthos (flower); she was a sea-nymph of Greek myth.
Delicate and floral, it is one of the prettiest of the classical nymph names.
Ianthe 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 Ianthe reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.