Along with Easter (deriving from Passover), Pentecost is the only Jewish feast to have found a place in the Christian calendar. The term comes from Gk. pentēkostē, “50th [day],” which was used in Hellenistic Judaism (Tob. 2:1; 2 Macc. 12:32). The reference is to the festival on the 50th day after Passover.
1. OT
In the OT Pentecost is a harvest festival at the end of the wheat harvest. The usual term for it is the Festival of Weeks (ḥag [haš]šābuʿôt, Exod. 34:22; Deut. 16:16, etc.), with reference to the seven …