Why is a 5 cent coin called a nickel?

Answer 1

It's actually a bit complicated. Nickel metal is heavily used for coins today because it's inexpensive and is very hard, so nickel coins don't wear out quickly. But when the Mint first starting making coins nickel couldn't be used because it was so hard it damaged the relatively primitive coin presses then in use.

By the middle of the 19th century Metallurgy had improved enough that the Mint started experimenting with making low-denomination coins out of an alloy of 25% nickel and 75% copper.

The first coins to use that alloy were a 3¢ piece in 1865. and a 5¢ piece the next year. At the same time the Mint also issued smaller coins with the same denominations but made of a silver alloy. To distinguish them, people started referring to them by their denominations and metal; e.g. "three cent silvers", "three cent nickels", and so on.

By 1873 the nickel coins had proven to be successful so the silver versions were discontinued, but people still talked about "three cent nickels" and "five cent nickels". The nickel 3¢ piece was discontinued 16 years later, leaving "five cent nickels" as the only coin remaining of the original four. The denomination was no longer needed to distinguish the coin, so its name was eventually shortened to just "nickel".