The word Pentecost is found in Acts 2:1; 18:21; 20:16. Pentecost is the same as the Feast of Weeks given in Leviticus 23:15-22, Exodus 34:22; and Deuteronomy 16:9-12, 16.
The word translated Pentecost in the New Testament means 50. In Leviticus 23 Feast of Weeks is prescribed to begin 50 days after the seventh Sabbath after Passover.
It is unclear whether part or all of the original New Testament manuscripts were written in Hebrew or Greek.
If the part involving Feast of Weeks was written in Hebrew, it would seem the Jews of New Testament days at least as an alternative used the Hebrew word for fifty to identify Feast of Weeks and the translators into Greek translated Feast of Weeks as Pentecost in Greek.
If the original was written in Greek, then it would seem the Jews of New Testament days used the Greek word for fifty at least as an alternative to identify Feast of Weeks.
Otherwise, one would have to conclude that the original New Testament manuscript has been tampered with and the word replaced in the Greek versions we have today. Therefore, it is not a translation issue but an original manuscript issue.
Reference:
Biblical Feasts
