turquoise

Turquoise comes from Middle French turquoise, from Old French (pierre) turquoise, meaning "Turkish (stone)," built from turc plus the suffix -ois. The stone itself was mined near Nishapur in the Khorasan region of Persia, but it reached Europe by way of Turkish traders, so it picked up their name rather than its actual source.

The word stuck to the stone even though the stone never came from Turkey itself — the name just marks the route it traveled to reach European hands.

It's a doublet of Turkish, since both trace back to the same root, turc. A similar pattern shows up in copper, which comes from Cyprus, the island Europeans associated with that metal.