The term Pentecost comes from the Greek Πεντηκοστή (Pentēkostē) meaning "fiftieth" (50th). It refers to the festival celebrated on the fiftieth day after Passover, also known as the "Feast of Weeks" in the Septuagint and the "Feast of 50 days" in rabbinic tradition.
Hope I Helped :)
- Hind