1) High-tensile steel product 2) Something hammers hit 
Piano wire, or `music wire`, is a specialized type of wire made for use in piano strings. It is made from tempered high-carbon steel, also known as spring steel, which replaced iron as the material starting in 1834. Piano wire has a very high tensile strength to cope with the heavy demands placed upon piano strings; accordingly, piano wire is al.....
[n] - thin steel wire of high tensile strength
High quality steel wire used for making springs.
noun thin steel wire of high tensile strength