Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† Pentēcostē, ēs, f., = πεντηκοστή (sc. ἡμέρα), the fiftieth day after Easter, WhitSunday, Pentecost (eccl. Lat.), Vulg. 2 Macc. 12, 32; id. 1 Cor. 16, 8; Tert. Idol. 14.