Old Prussian is an extinct Baltic language, once spoken by the Old Prussians, the indigenous peoples of Prussia (not to be confused with the later and much larger German state of the same name), now northeastern Poland and the Kaliningrad Oblast of Russia.

The language is called Old Prussian to avoid confusion with the German dialects Low Prussian and High Prussian, and the adjective Prussian, which is also often used to relate to the later German state.

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