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Easter, or Eastre as it is originally, was the name of a pagan goddess of the dawn whose festival was held on the vernal equinox. The Christians adopted her name and many of the celebratory practices (as they did with Saturnalia and Christmas) for their celebration of Christ’s resurrection. The pagan holiday roughly corresponded with the time of year of the crucifixion and resurrection (Passover).

From the translation of Bede’s Ecclesiastical History commonly attributed to King Alfred, c.890:

Ic ðas tide Eastrena ecelice healdan wille.
(I will eternally celebrate Easter)

(Source: Oxford English Dictionary, 2nd Edition)