Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Pŏlyhymnĭa (Pŏlymnĭa, Poët. ap. Anth. Lat. 1, p. 51 Burm.), ae, f., = Πολυμνία (she of many hymns), one of the Muses, Hor. C. 1, 1, 33; Ov. F. 5, 9; Mart. 4, 31, 7; Aus. Idyll. 20.