I.e., "fiftieth", found only in the New Testament (Acts 2:1; 20:16; 1 Corinthians 16:8). The festival so named is first spoken of in Exodus 23:16 as "the feast of harvest," and again in Exodus 34:22 as "the day of the firstfruits" (Numbers 28:26). From the sixteenth of the month of Nisan (the second day of the Passover), seven complete weeks, i.e., forty-nine days, were to be reckoned, and this feast was held on the fiftieth day. The manner in which it was to be kept is described in Leviticus 23:15-19; Numbers 28:27-29. Besides the sacrifices prescribed for the occasion, every one was to bring to the Lord his "tribute of a free-will offering" (Deuteronomy 16:9-11). The purpose of this feast was to commemorate the completion of the grain harvest. Its distinguishing feature was the offering of "two leavened loaves" made from the new corn of the completed harvest, which, with two lambs, were waved before the Lord as a thank offering.
The day of Pentecost is noted in the Christian Church as the day on which the Spirit descended upon the apostles, and on which, under Peter's preaching, so many thousands were converted in Jerusalem (Acts 2).