From 紅葉(もみじ) (momiji, “autumn leaf”) + 卸(おろ)し (oroshi, 連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 卸(おろ)す (orosu).).
もみじおろし • (momiji-oroshi) ←もみぢおろし (momidiorosi)?