Hail Dawn, goddess of many names!
Éostre (Old English, West Saxon dialect) AY-aw-streh (ay as in say, aw as in awe)
Éastre (Old English, Northumbrian dialect). AY-ah-streh (ay as in say)
Both forms are used by contemporary pagans. Occasionally—probably under the influence of Ostara—written Oestre. (Technically, this form is historically incorrect, if you care about such things.)
*Ôstarâ (Old High German) OH-sta-ra (but most English-speakers say oh-STAR-a; technically, this is historically incorrect, if you care about such things.)
Name reconstructed by the Brothers Grimm. Probably the most frequently-used name for the goddess, and her springtime festival, among contemporary pagans and heathens.
*Austra (Old Norse)
Name reconstructed by the Brothers Grimm. We have no evidence that the Norse knew of this goddess. If they did, this is what they would have called her.
*Austrô (Gothic)
Name reconstructed by the Brothers Grimm. We have no evidence that the ancient Goths (as distinguished from the modern ones) knew of this goddess. If they did, this is what they would have called her.
*Austrô (Proto-Germanic) (ca. 500 BCE)
This is the Germanic form of the pan-Indo-European Dawn Goddess also called Ushas (Sanskrit), Êôs (Greek), Aurôra (Latin), Aušrine (Lithuanian), Austra (Latvian), and by many other names.
Easter (Modern English)
Words are political.
Although the majority of English-speaking Paganry has taken Ostara as its term of art—I suspect that Eostre and Eastre seem 'tainted' by their proximity to overculture use—some heathens have taken to calling the Lady of Dawn—and her eponymous spring festival—by her modern name, Easter. (For what it's worth, Neil Gaiman does the same in American Gods.)
For all that this usage may occasion confusion to some listeners, it's indisputable that, had the worship of the Anglo-Saxon gidden (goddess) continued unbroken into our times, we would today name her Easter.
So cavil if you like. It's our word, and I for one am not giving it up.
And it sure does make buying cards easier.
The blessings of the every-young Lady of Spring be upon you.
Whatever you call Her.
Above: Nicholas Roerich, The Rite of Spring (1945)