rotochute
/ˈrəʊtə(ʊ)ʃuːt/noun
A mechanical device for slowing the speed of an object falling through the air or through water, consisting of a set of blades that rotate as a result of the downward motion; a buoy or other object fitted with such a device.
Origin
1940s (in an earlier sense). Apparently from roto- + -chute, although in sense 1 the semantic motivation is unclear.