Silesia vs Slask

Silesia and Slask both are nouns.

Word	Noun	Adjective	Verb	Adverb
Silesia	Yes	No	No	No
Slask	Yes	No	No	No

As nouns, Silesia and Slask are synonyms defined as:

Silesia and Slask: a region of central Europe rich in deposits of coal and iron ore; annexed by Prussia in 1742 but now largely in Poland

Other synonyms of Silesia include Schlesien, Slezsko.

Silesia (noun)	Slask (noun)
a region of central Europe rich in deposits of coal and iron ore; annexed by Prussia in 1742 but now largely in Poland	a region of central Europe rich in deposits of coal and iron ore; annexed by Prussia in 1742 but now largely in Poland