Which knot is not considered to be a hitch?

The sheepshank knot is designed to shorten a rope without cutting it and is primarily used to secure a length of line by creating two loops in the standing part of the rope, which distinguishes it from hitches. A hitch, by definition, is a knot that attaches a rope to an object, while the sheepshank does not perform this function, making it a different category of knot.

On the other hand, the bowline forms a fixed loop at the end of a line, the clove hitch is specifically designed to fasten a rope to a post or other object, and the half hitch is often used to secure lines to objects or to other lines. Each of these knots has a primary function related to securing, tethering, or attaching, which fits the definition of hitches.