Gerhard Kittle, Theological Dictionary Of The New Testament, Vol. II. (Grand Rapids: Eerdmans, 1965), 901-904."In Christian usage EASTER is called pascha" (page 897). "The oldest accounts of a Christian Paschal feast take us back to the apostolic period. The N.T. tells us nothing about the details, but the gaps may be filled in from accounts of the Quartodecimans, since their EASTER, as we now know, was a direct continuation of that of the primitive Church." (page 901). "The paschal feast thus took place in the primitive Church at the same time as the Jewish Passover, that is, on the night of the 15th Nisan...Hence the original Christian EASTER, as we have come to know and deduce it from the Quartodeciman sources, shared with the Jewish Passover not only the time and details of the rite but also the expectation of the Messiah...The first assured reference to a Sunday EASTER is in 155 A.D., but it was probably much older than this." (pages 902-903)
From the article "Should it be Passover or Easter?"
There is no doubt that paska means Easter in modern Greek. The charge, however, is that it did not mean Easter until centuries after the composition of Acts 12:4. This is not true. In the Gospel of John there is already a distinction being made between the Christian paska and the Jewish paska. One of the words for Passover in modern Greek is paska (Passover of the Jews). We see this same phrase already in the time of John the Apostle:
John 2:13: And the Jews' passover was at hand.
John 11:55: And the Jews' passover was nigh at hand.
The fact that John writes, "Jews Pascha" indicates that there was a need to qualify the word Pascha for the immediate audience of John's Gospel. Such a phrase would be redundant unless there were already a distinction between a Jew's Pascha and another Pascha. Apparently within the first century, Christians had already appropriated the word Pascha to refer to the Christian celebration of the resurrection.
Source:
Another King James Bible Believer