Old English Pentecosten "Christian festival on seventh Sunday after Easter," from Late Latin pentecoste, from Greek pentekoste (hemera) "fiftieth (day)," fem. of pentekostos, from pentekonta "fifty," from pente "five" (from PIE root *penkwe- "five"). The Hellenic name for the Old Testament Feast of Weeks, a Jewish harvest festival observed on 50th day of the Omer (see Leviticus xxiii.16).
