Sentence:  <WSD>Gunmetals</WSD> are alloys of copper, tin and zinc, formerly used for casting cannon. With lead additions they become suitable as bearing materials and are called leaded <WSD>gunmetals</WSD> (the US term is leaded red brass); they are quite often misnamed bronzes. 
Meaning of the word marked with <WSD> tags:  An alloy of 88% copper, 10% tin and 2% zinc, originally used for making guns.