Толковый словарь английского языка Oxford English Reference - pentecost

n. 1 a Whit Sunday. b a festival celebrating the descent of the Holy Spirit on Whit Sunday. 2 a the Jewish harvest festival, on the fiftieth day after the second day of Passover (Lev. 23:15-16). b a synagogue ceremony on the anniversary of the giving of the Law on Mount Sinai. Etymology: OE pentecosten & OF pentecoste, f. eccl.L pentecoste f. Gk pentekoste (hemera) fiftieth (day)