Where does the word Easter come from?

There is no reference to the word Easter in the New Testament. Nor does it feature in most translations of the Bible into vernacular languages. Most use a derivation of the Jewish feast of Passover - rooting the key events in their historical and religious context (in Spanish 'pascua', for example). 

In other languages there is typically more linguistic emphasis on the idea of Holy Week (Semana Santa in Spanish, for example).

So why Easter in English? Scholars agree that the origin is pre-Christian and pagan rather than strictly Biblical. Beyond that there is little consensus.
The most popular theory is reflected in the entry for Easter in the Canadian Oxford Dictionary:

Old English ēastre, after a Germanic goddess Eostre; related to Old High German ōstarūn Easter, Old Norse austr to the east, Old Slavonic ustru like summer.
According to this explanation, the Old English word eastre came Eostre, "a goddess associated with spring."
Further elaboration is found in a work written in AD 725 by Saint Bede, an English monk and historian. According to Bede, April was called Eosturmonath ("Easter-month") because in pagan times the month was dedicated to Eostre, an Anglo-Saxon goddess of spring. 
Ostara (1884) by Johannes Gehrts

When Christian beliefs spread throughout England, says Bede, Easter-month lent its name to the new April festival.

Another theory is that Eostre was simply the Anglo-Saxon word for spring festivals. Linguists trace this word to roots thousands of years old meaning "shine" and "dawn." Spring is a season of lengthening days and increased light. It would make sense for early peoples to give their spring festivals a name that celebrated the rising sun. Source

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Introductory Dictionary of Theology and Religious Studies