Masuria - Mazury

 Masuria (Polish: Mazury, German: Masuren, Masurian: Mazurÿ) is a historical region in northern and northeastern Poland, famous for its 2,000 lakes. The region covers a territory of some 10,000 km2 which is inhabited by approximately 500,000 people.

Kestutis or Kęstutis

 Kęstutis (1297–1382) was the Grand Duke of Lithuania. He was the Duke of Trakai and governed the Grand Duchy of Lithuania, 1342–1382, together with his brother Algirdas (until 1377) and his nephew Jogaila (until 1381). He ruled over the Lithuanians and Ruthenians.

Gord

 A gord is a medieval Slavonic fortified settlement usually built on strategic sites such as hilltops, riverbanks, lake islets or peninsulas between the 6th–12th centuries in Central and Eastern Europe. The typical gord usually consisted of a group of wooden houses surrounded by a wall made of earth and wood and a palisade running along the top of the bulwark.

Moczydoly

 Moczydoły is a fictional property of Zych, Jagienka's father. The name is after wetlands on the property.

Mead or honey

Mead is an alcoholic beverage made by fermenting honey mixed with water, and sometimes with added ingredients such as fruits, spices, grains, or hops. The alcoholic content ranges from about 3.5% to more than 20%. The defining characteristic of mead is that the majority of the beverage's fermentable sugar is derived from honey.

The term honey wine (or 'honey' in the book) is sometimes used as a synonym for mead.

Mead was produced in ancient times throughout Europe, Africa and Asia.

Dwor (dwór)

Dwór: court, the residence of a sovereign, manor, estate, farmstead, homestead.

or

Dwór: collective body of the retinue of a sovereign; formal assembling of the retinue of a sovereign.

Zych from Zgorzelice

 Zych from Zgorzelice is a neighbor of Macko and Zbyszko and father of Jagienka.

Tatars

 The Tatars is an umbrella term for different Turkic ethnic groups bearing the name "Tatar." Initially, the ethnonym Tatar possibly referred to the Tatar confederation. That confederation was eventually incorporated into the Mongol Empire when Genghis Khan unified the various steppe tribes. 

Historically, the term Tatars (or Tartars) was applied to anyone originating from the vast Northern and Central Asian landmass then known as Tartary. This term was also conflated with the Mongol Empire itself. More recently, however, the term has come to refer more narrowly to related ethnic groups who refer to themselves as Tatars or who speak languages that are commonly referred to as Tatar, namely Tatar by Volga Tatars (Tatars proper), Crimean Tatar by Crimean Tatars, and Siberian Tatar by Siberian Tatars.

Jasko of Teczyn, Castellan of Krakow

 In the book Jasko of Teczyn is a Catellan of Krakow.

Jan (or Jasko) of Teczyn, (born between 1408–1410, died on July 6, 1470) - the castellan of Kraków in the years 1459–1470, the voivode of Kraków in the years 1438–1459, the voivode of Sandomierz in the years 1437–1438, the castellan of Wojnica in the years 1435–1437, guardian of the Kraków land in the years 1434–1436, the starost of Lublin in the years 1434–1438, the castellan of Biecz in the years 1433–1435.

For a quarter of a century, he was the most powerful magnate in Poland. It seems that the book's character is based on Jan, but the story itself takes place around 1410.

Rus'

More precisely - Kievan Rus'

Kievan Rus' was a loose federation in Eastern Europe and Northern Europe from the late 9th to the mid-13th century. Encompassing a variety of peoples, including East Slavic, Norse, Baltic, and Finnic. It was ruled by the Rurik dynasty. The modern nations of Belarus, Russia, and Ukraine all claim Kievan Rus' as their cultural ancestors, with Belarus and Russia deriving their names from it. At its greatest extent in the mid-11th century, Kievan Rus' stretched from the White Sea in the north to the Black Sea in the south and from the headwaters of the Vistula in the west to the Taman Peninsula in the east, uniting many East Slavic tribes.