Old Prussian

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The Baltic language of eastern Prussia that became extinct in the 1700s.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Of or pertaining to the Old Prussian language or people.
• proper noun the Baltic language spoken by the people of Prussia prior to their subjugation by the German Order.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a dead language of the (non-German) Prussians (extinct after 1700); thought to belong to the Baltic branch of Indo-European