from google... The naming of the celebration as “Easter” seems to go back to the name of a pre-Christian goddess in England, Eostre, who was celebrated at beginning of spring.

A common explanation is that there was a festival in springtime for a goddess with a name that sounds vaguely like "Easter" (Eoster). When the people in the area changed to Christianity, they changed the focus of the festival, but kept the name and some of the rituals.