In Acts 12:4 of the King James Version of the Bible is recorded: "And when he had apprehended him, he put him in prison, and delivered him to four quaternions of soldiers to keep him; intending after Easter to bring him forth to the people."
This verse of Scripture has excited much discussion -- often more than it should and of a nature that is not edifying. Now I add my voice to the discussion, but hopefully in soft rather than shrill tones that might edify the dear reader. Acts 12:4 has provided the anti-KJV-ist ample fodder to rail against the King James translation. It has incited the KJV-Onlyist to create tortured explanations of why "Easter" is correct and "Passover" would be incorrect (in this one verse). The whole of it is rather simple and could be dismissed rather easily were it not for the extremists.
First, barring finding some source where the King James translators have explained it, we don't really know why they chose to translate "paska" as Easter in this passage while translating it as Passover is the other verses where it is used.
Second, a little knowledge of the development of the English language and the history of English translations apprises us that there is nothing sinister, secret or stupid going on with the translation. Rather, it is quite simple.
Englishmen had no Jewish background but were converted to Christianity from paganism. They had no word for the Old Testament feast of Passover, and identified the New Testament Passover with the resurrection of Jesus Christ and what they called Ester/Easter. The first English translator, Wycliffe, used "paske" here, basically transliterating it over from the Greek or Latin. On the other hand, nearly 200 years later when Tyndale translated the New Testament, he chose "ester",* a word that was in common usage at that time. The word "Passover," which is current in most modern translations, did not exist at that time. In fact, it was Tyndale himself who coined the word "Passover" when he translated the Old Testament from Hebrew into English. Possibly he felt that using "Easter/Ester" was taking something back from the New Testament and transposing it inappropriately on the old. Regardless, he is the source of the word "Passover".
As translation and language progressed, the use of Easter for Passover in the New Testament dwindled. By the time of the 1568 Bishops' Bible "Easter" is used only twice (here and John 11:55). With the coming of the King James, "Easter" was left with one solitary use.
Why did the King James translators not change it to "Passover" in Acts 12:4 as in all the other cases? Was it an editorial oversight? Did they see something that caused them to think it was better left in place? We'll probably never know. Rather than worry over or fight about it, just know that the context indicates that Easter refers to the Passover season.
* my count using StudyLight.org is 24 times in 23 verses in the New Testament