Quartodeciman Dispute (Easter Controversy)

Controvery in the 1st & 2nd century of the Christian Church over what day Passover-hence "Easter" (called Pascha) should fall on. In the east it was held for many years longer than in the west on 14 Nissan. Which means it could fall on any day of the week each year. But in the west, under the influence of the Bishop of Rome (Pope), it gradually became associated with the 1st day of the week, Sunday.

Bisshop Sixtus I of Rome began to keep it on Sunday (Pope from 115 AD-125AD). "Quartodectimanism, prevalent in Asia Minor and Syria in
the second century, emphasized the death of Christ, the true
Paschal victim (JN 18:28; 19:42), while Roman practice emphasized
the observance of Sunday as the day of the Resurrection ..."Catholic Encyclopedia

Irenaeus tells us that Polycarp, a disciple of John, was a quartodeciman. (Prefered 14 Nisan). Anicetus replaced Sixtus on the Papal throne in 155AD. Here is what Irenaeus says happened when the two met to discuss the situation:

"Anicetus could not persuade Polycarp to forgo the [Quartodeciman] observance inasmuch as these things had been always observed by John the disciple of the Lord, and by other apostles with whom he had been conversant; nor did Polycarp persuade Anicetus to keep it: Anicetus said that he must hold to the way of the elders before him."

In the 190's AD, Pope Victor I was on the Papal throne in Rome. He tried to enforce Sunday as "Easter" instead of 14 Nisan and went as far as to try to excommunicate those bishops who resisted. But he was strongly rebuked by some of the other bishops and the policy was reversed. (Note-the Bishop of Rome, at an early date, trying to enforce "Sunday" as a special day on others-but his time was not yet). Years later in the east, John Chrysostom harassed those who kept 14 Nisan. Also, the Celtic Church, which resisted becoming part of the Catholic Church well into the early Middle Ages, were said to be quartodecimans by Wilfrid, bishop of York in England.
“For I received of the Lord that which also I delivered unto you, that the Lord Jesus the same night in which he was betrayed [not Easter Sunday] took bread” (1 Corinthians 11:23). Keep in mind Jesus Christ was betrayed during the night of Nisan 14 (Luke 22:15-22), which was the day of Passover (Exodus 12:6-13)." From Passover to Easter
As for "Easter" itself:

“Easter” actually originates with the pagan worship of Ishtar (or Astarte) that was traditionally observed at the time of the vernal equinox, nominally about March 21 or 22. Traditional pagan fertility symbols of both rabbits and eggs continue to be associated with this holiday. The practice of those Christians insisting on celebrating Passover on the fourteenth day of Nisan from the Old Testament calendar¹ was known as Quartodecimanism (“fourteenism,” as derived from Latin). The council unanimously ruled that the Easter festival should be celebrated throughout the Christian world on the first Sunday after the full moon following the vernal equinox; and that if the full moon should occur on a Sunday, and thereby coincide with the Passover festival, Easter should be commemorated on the following Sunday. As a result of the Council of Nicea, and amended by numerous subsequent meetings, the formal church deliberately attempted to design a formula for “Easter” which would avoid any possibility of it falling on the Jewish Passover, even accidentally! In 387, for example, the dates of Easter in France and Egypt were 35 days apart. About 465, the church adopted a system of calculation proposed by the astronomer Victorinus, who had been commissioned by Pope Hilarius to reform the calendar and fix the date of Easter. Elements of his method are still in use, although the Scythian monk Dionysius Exiguus made significant adjustments to the Easter cycle in the 6^th century." Traditional Myths
"The modern English term Easter developed from the Old English word Ēastre or Ēostre which itself developed prior to 899. The name refers to Eostur-monath (Old English "Ēostre month"), a month of the Germanic calendar attested by Bede, who writes that the month is named after the goddess Ēostre of Anglo-Saxon paganism. Bede notes that Ēostur-monath was the equivalent to the month of April, yet that feasts held in her honor during Ēostur-monath had gone out of use by the time of his writing and had been replaced with the Christian custom of the "Paschal season"."Wikipedia

For even Christ our passover is sacrificed for us:

1Corinthians 5:7