That which destroys something.
A larger warship with guided missile armament, usually intended for air defence or anti-ship roles. Often, but not always, larger than a frigate and smaller than a cruiser.
A small, fast warship with light gun armament, smaller than a cruiser, but bigger than a frigate.
A person who commits multiple (more than two) murders, especially similar ones with no obvious motive over a period of time with a "cooling-off" period between each murder.