[Greek helix, helik-, spiral.]
A helix is a spiral formed by a wire wound in a single layer around a cylinder or cone, with constant pitch. Something helical is spiral in shape, but something helicoid is more specifically in the form of a helix. A helicopter (Greek pteron, a wing) is an aircraft with a rotating wing that behaves like a screw propeller. The plant called the helichrysum (Greek khrusos, gold) has yellow spiral flowers.