Well, the Canadian "nickel" is now steel and they still call it the nickel.
As was posted above, the original
Flying Eagle cent was called a "Nickel" due to the nickel content. This made it whiter in appearance than the large copper cents it replaced. The cent reverted to an almost pure (95%) copper format and the copper color returned.
Next, the cupro-nickel 3-cent coin was introduced and this was called a "nickel" to distinguish it from the silver 3-cent coin.
After the cupro-nickel 5-cent coin came along the name transitioned over to it. To this day the same 25% nickel/75% copper composition is used, making the Nickel the coin with the oldest composition. All other circulating coins have changed composition in the 20th century, the nickel (save for the 42-45 wartime silver mix) has remained the same. The nickel is also the only circulating coin that is actually a single alloy, since 1982 all the other coins are either clad or plated.