Today, the United States nickel coin is made of a 100 percent copper center, with a surface made of 25% nickel and 75% copper. But this wasn't always the case. In the past, the nickel was called a half disme and was made from silver. Disme is pronounced the same way as the word dime.
The first nickel in the United States was actually worth three cents, because the postage price to mail a letter dropped from five cents to three cents in 1851. It was made of silver. When the Civil War hit, a new version of this three cent coin was made with nickel and copper in order to prevent silver hoarding. Since the word copper was already used as a nickname for a one cent coin, the word nickel was used for this three cent coin.
In 1866, the value of silver was significantly greater than gold, so people hoarded silver coins and caused a shortage. This prompted the US Mint to introduce the shield nickel, which was made of 75 percent copper and 25 percent nickel. As the years passed new nickels were introduced, but they consisted of design changes, not changes in composition.
The nickel used today was first minted in 1938, and included the image of Thomas Jefferson. Between the years 1938 and 1942, this nickel had the same diameter, weight and composition as the buffalo nickel. During World War II there was a shortage of nickel, so the composition of the Jefferson nickel changed to silver, copper, and manganese. In 1946, after the war was over, the Mint resumed the traditional five cent coin composition of copper and nickel, which is still used today.