The Collaborative International Dictionary of English v.0.48:
Polyhymnia \Pol`y*hym"ni*a\, n. [L., from Gr. ?; poly`s many + ? hymn.] (Anc. Myth.) The Muse of lyric poetry. [1913 Webster]WordNet (r) 3.0 (2006):
Polyhymnia n 1: (Greek mythology) the Muse of singing and mime and sacred dance