'Big Indian' brand carbon steel sickle knife for cutting hay, grain or corn... this is probably late 1800s at our best guess, based on the forged construction and beehive style wooden handle.
Measures about 11 1/2" straight across the curved blade. It has good clear embossing, and is in very good condition overall. This does need sharpening, but it doesn't look as though it's had a lot of use.