Flat-iron gunboats were a number of classes of coastal gunboats generally characterised by small size, low freeboard, the absence of masts, and the mounting of a single non-traversing large gun, aimed by pointing the vessel. They acquired their nickname from the physical similarity with the flat iron used for ironing clothes during the 19th century.

A clothes iron is a small appliance that, when heated, is used to press clothes to remove wrinkles and unwanted creases. Domestic irons generally range in operating temperature from between 121 °C (250 °F) to 182 °C (360 °F). It is named for the metal (iron) of which the device was historically made, and the use of it is generally called ironing, the final step in the process of laundering clothes.