It's most likely for a Liberty engine and was probably used on one of the Navy flying boats in the late teens and early twenties. It's a fairly common design, and Unico was one of the many known suppliers of propellers at that time.
It's half of a 4-blade assembly. The notch on the rear locked into an identical blade with a notch on the front. Here's a similar one, but a 2 blade design with different geometry.
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