A screw steamer or screw steamship is an old term for a steamship or steamboat powered by a steam engine, using one or more propellers (also known as screws) to propel it through the water. Such a ship was also known as an "iron screw steam ship". In the 19th century, this designation was normally used in contradistinction to the paddle steamer, a still earlier form of steamship that was largely, but not entirely, superseded by the screw steamer.