It's well know that Easter is named after Eostre.,an Old English pagan goddess of spring.
Except maybe not. We only know of a single reference to this goddess. Bede, writing in the early 8c, had this to say (Bede wrote in Latin, this is Copilot's translation)
“Eostur-monath, which is now interpreted as the Paschal month, once took its name from their goddess who was called Eostre, in whose honour they heldfestivals in that month. From her name they now call the Paschal season by the old observance’s customary name, calling the joys of the new solemnity by the title of the ancient rite.”
Because this goddess is not known from anywhere else until mentioned by Jacob Grimm (language scholar and with his brother Wilhelm collector of the fairy tales that bear the brothers' name), in 1835, some scholars have suggested Bede may just have been theorising her existence to explain why the English called the festival Easter instead of Pasca, which means 'Passover' and is the name used today in much of Europe.
English is not unique, because the German is Ostern, which is evidently from the same root, but doesn't of itself cast any light on the whether there was ever a Germanic goddess Eostre
What alternative theories are there? The OED suggests the word is cognate with east, and with Latin aurora, Greek eos (εος), etc. etc. 'dawn'.
Etymonline connects it to a PIE root *aus-, 'shining', which is also the origin of Australia, because (confusingly) austral means 'to the south'. The semantics of this are all to do with shining, and south is thought to share a PIE root with sun, so it does seem plausible.
If this explanation is true, it means that — very surprisingly — 'Easter' and 'Oz' are etymologically related!
Going back to Eostre, what kind of evidence might we one day find that would corroborate Bede? We'd need something written before Bede (otherwise it might have just been borrowed from Bede, whose works were well-known in the middle ages). I suppose the gold standard, as you might call it, would be for archaeologists to uncover a secuely dateable inscription in Runic characters that referred to Eostre in a description of a pre-Christian religious observance, or a charm, such as the 'Nine Herbs Charm' which unambiguously mentions Woden (rather gratuitously killing an adder, from what I can make out.)
In case you are interested, here is how the name Eostre would be written in Old English runes known as Futhorc.
ᛖᚩᛋᛏᚱᛖ
See Comments for picture credit and further notes.
Comments
Notes
The picture of Bede at work is from a copy of his Life of St Cuthbert and is in the public domain.
For more about Bede see the Wikipedia article 'Bede'.
For more about the Nine Herbs Charm see the wikipedia arsine ‘Nine_Herbs_Charm’
Grimms description of Eostre