From 振(ふ)り (furi, “連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 振(ふ)る (furu).”) + 鼓(つづみ) (tsuzumi).
ふりつづみ • (furitsuzumi) ←ふりつづみ (furitudumi)?