Ostara
Around 20 March
The name comes from Eostre, a goddess Bede mentions in a single eighth-century passage explaining the English name for the Paschal month. No other early source names her, which has made her the subject of a century of scholarly argument.
The modern festival is largely a twentieth-century construction built on that one line, which does not make it less meaningful to those who keep it, only younger than it is often claimed to be.
Equinox observance itself is ancient and well-attested archaeologically across Europe, whatever anyone called it.